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Juvenile hormone (JH) plays vital roles in insect reproduction, development, and in many aspects of physiology. JH primarily acts at the gene-regulatory level through interaction with an intracellular receptor (JHR), a ligand-activated complex of transcription factors consisting of the JH-binding protein Methoprene-tolerant (MET) and its partner Taiman (TAI). Initial studies indicated significance of post-transcriptional phosphorylation, subunit assembly, and nucleocytoplasmic transport of JHR in JH signaling. However, our knowledge of JHR regulation at the protein level remains rudimentary, partly due to the difficulty of obtaining purified, functional JHR proteins. Here we present a method for high-yield expression and purification of JHR complexes from two insect species, the beetle Tribolium castaneum and the mosquito Aedes aegypti. Recombinant JHR subunits from each species were co-expressed in an insect cell line using a baculovirus system. MET-TAI complexes were purified through affinity chromatography and anion exchange columns to yield proteins capable of binding both the hormonal ligand (JH III) and DNA bearing cognate JH-response elements. We further examined the beetle JHR complex (TcJHR) in greater detail. Biochemical analyses and mass spectrometry confirmed that TcJHR was a 1:1 heterodimer consisting of TcMET and TcTAI proteins, stabilized by the JHR agonist ligand methoprene. Phosphoproteomics uncovered multiple phosphorylation sites in the TcMET protein, some of which were induced by methoprene treatment. Finally, we report a functional bipartite nuclear localization signal, straddled by phosphorylated residues, within the disordered C-terminal region of TcMET. Our present characterization of the recombinant JHR is an initial step towards understanding JHR structure and function.

The functionalization of proteins with different cargo molecules is highly desirable for a broad range of applications. However, the reproducible production of defined conjugates with multiple functionalities is a significant challenge. Herein, we report the dual site-specific labeling of an antibody fragment, utilizing the orthogonal Sortase A and π-clamp conjugation methods, and demonstrate that binding of the antibody fragment to its target receptor is retained after dual labeling.

Mature red blood cells (RBCs) lack internal organelles and canonical defense mechanisms, making them both a fascinating host cell, in general, and an intriguing choice for the deadly malaria parasite Plasmodium falciparum (Pf), in particular. Pf, while growing inside its natural host, the human RBC, secretes multipurpose extracellular vesicles (EVs), yet their influence on this essential host cell remains unknown. Here we demonstrate that Pf parasites, cultured in fresh human donor blood, secrete within such EVs assembled and functional 20S proteasome complexes (EV-20S). The EV-20S proteasomes modulate the mechanical properties of naïve human RBCs by remodeling their cytoskeletal network. Furthermore, we identify four degradation targets of the secreted 20S proteasome, the phosphorylated cytoskeletal proteins β-adducin, ankyrin-1, dematin and Epb4.1. Overall, our findings reveal a previously unknown 20S proteasome secretion mechanism employed by the human malaria parasite, which primes RBCs for parasite invasion by altering membrane stiffness, to facilitate malaria parasite growth., Plasmodium falciparum secretes extracellular vesicles (EVs) while growing inside red blood cells (RBCs). Here the authors show that these EVs contain assembled and functional 20S proteasome complexes that remodel the cytoskeleton of naïve human RBCs, priming the RBCs for parasite invasion.

STUDY QUESTION How is endometrial epithelial receptivity, particularly adhesiveness, regulated at the luminal epithelial surface for embryo implantation in the human? SUMMARY ANSWER Podocalyxin (PCX), a transmembrane protein, was identified as a key negative regulator of endometrial epithelial receptivity; specific downregulation of PCX in the luminal epithelium in the mid-secretory phase, likely mediated by progesterone, may act as a critical step in converting endometrial surface from a non-receptive to an implantation-permitting state. WHAT IS KNOWN ALREADY The human endometrium must undergo major molecular and cellular changes to transform from a non-receptive to a receptive state to accommodate embryo implantation. However, the fundamental mechanisms governing receptivity, particularly at the luminal surface where the embryo first interacts with, are not well understood. A widely held view is that upregulation of adhesion-promoting molecules is important, but the details are not well characterized. STUDY DESIGN, SIZE, DURATION This study first aimed to identify novel adhesion-related membrane proteins with potential roles in receptivity in primary human endometrial epithelial cells (HEECs). Further experiments were then conducted to determine candidates’ in vivo expression pattern in the human endometrium across the menstrual cycle, regulation by progesterone using cell culture, and functional importance in receptivity using in vitro human embryo attachment and invasion models. PARTICIPANTS/MATERIALS, SETTING, METHODS Primary HEECs (n = 9) were isolated from the proliferative phase endometrial tissue, combined into three pools, subjected to plasma membrane protein enrichment by ultracentrifugation followed by proteomics analysis, which led to the discovery of PCX as a novel candidate of interest. Immunohistochemical analysis determined the in vivo expression pattern and cellular localization of PCX in the human endometrium across the menstrual cycle (n = 23). To investigate whether PCX is regulated by progesterone, the master driver of endometrial differentiation, primary HEECs were treated in culture with estradiol and progesterone and analyzed by RT-PCR (n = 5) and western blot (n = 4). To demonstrate that PCX acts as a negative regulator of receptivity, PCX was overexpressed in Ishikawa cells (a receptive line) and the impact on receptivity was determined using in vitro attachment (n = 3–5) and invasion models (n = 4–6), in which an Ishikawa monolayer mimicked the endometrial surface and primary human trophoblast spheroids mimicked embryos. Mann–Whitney U-test and ANOVA analyses established statistical significance at *P ≤ 0.05 and **P ≤ 0.01. MAIN RESULTS AND THE ROLE OF CHANCE PCX was expressed on the apical surface of all epithelial and endothelial cells in the non-receptive endometrium, but selectively downregulated in the luminal epithelium from the mid-secretory phase coinciding with the establishment of receptivity. Progesterone was confirmed to be able to suppress PCX in primary HEECs, suggesting this hormone likely mediates the downregulation of luminal PCX in vivo for receptivity. Overexpression of PCX in Ishikawa monolayer inhibited not only the attachment but also the penetration of human embryo surrogates, demonstrating that PCX acts as an important negative regulator of epithelial receptivity for implantation. LIMITATIONS, REASONS FOR CAUTION Primary HEECs isolated from the human endometrial tissue contained a mixture of luminal and glandular epithelial cells, as further purification into subtypes was not possible due to the lack of specific markers. Future study would need to investigate how progesterone differentially regulates PCX in endometrial epithelial subtypes. In addition, this study used primary human trophoblast spheroids as human embryo mimics and Ishikawa as endometrial epithelial cells in functional models, future studies with human blastocysts and primary epithelial cells would further validate the findings. WIDER IMPLICATIONS OF THE FINDINGS The findings of this study add important new knowledge to the understanding of human endometrial remodeling for receptivity. The identification of PCX as a negative regulator of epithelial receptivity and the knowledge that its specific downregulation in the luminal epithelium coincides with receptivity development may provide new avenues to assess endometrial receptivity and individualize endometrial preparation protocols in assisted reproductive technology (ART). The study also discovered PCX as progesterone target in HEECs, identifying a potentially useful functional biomarker to monitor progesterone action, such as in the optimization of progesterone type/dose/route of administration for luteal support. STUDY FUNDING/COMPETING INTEREST(S) Study funding was obtained from ESHRE, Monash IVF and NHMRC. LR reports potential conflict of interests (received grants from Ferring Australia; personal fees from Monash IVF Group and Ferring Australia; and non-financial support from Merck Serono, MSD, and Guerbet outside the submitted work. LR is also a minority shareholder and the Group Medical Director for Monash IVF Group, a provider of fertility preservation services). The remaining authors have no potential conflict of interest to declare. TRIAL REGISTRATION NUMBER NA.

Bacterial collagen-like proteins differ from vertebrate collagens in that they do not contain hydroxyproline, which is seen as a characteristic of the vertebrate collagens, and which provides a significant contribution to the stability of the collagen triple-helix at body temperature. Despite this difference, the bacterial collagens are stable at around body temperature through inclusion of other stabilising sequence elements. Another difference is the lack of aggregation, and certain vertebrate collagen binding domains that can be introduced into the bacterial sequence lack full function when hydroxyproline is absent. In the present study we have demonstrated that a simple method utilising co-translational incorporation during fermentation can be used to incorporate hydroxyproline into the recombinant bacterial collagen. The presence and amount of hydroxyproline incorporation was shown by amino acid analysis and by mass spectrometry. A small increase in thermal stability was observed using circular dichroism spectroscopy. STATEMENT OF SIGNIFICANCE: Recombinant bacterial collagens provide a new opportunity for biomedical materials as they are readily produced in large quantity in E. coli. Unlike animal collagens, they are stable without the need for inclusion of a secondary modification system for hydroxyproline incorporation. In animal collagens, however, introduction of hydroxyproline is essential for stability and is also important for functional molecular interactions within the mammalian extracellular matrix. The present study has shown that hydroxyproline can be readily introduced into recombinant S. pyogenes bacterial collagen through direct co-translational incorporation of this modified imino acid during expression using the codons for proline in the introduced gene construct. This hydroxylation further improves the stability of the collagen and is available to enhance any introduced molecular functions.

Plasmodium falciparum exports hundreds of virulence proteins within infected erythrocytes, a process that requires cleavage of a pentameric motif called Plasmodium export element or vacuolar transport signal by the endoplasmic reticulum (ER)-resident protease plasmepsin V. We identified plasmepsin V-binding proteins that form a unique interactome required for the translocation of effector cargo into the parasite ER. These interactions are functionally distinct from the Sec61-signal peptidase complex required for the translocation of proteins destined for the classical secretory pathway. This interactome does not involve the signal peptidase (SPC21) and consists of PfSec61, PfSPC25, plasmepsin V and PfSec62, which is an essential component of the post-translational ER translocon. Together, they form a distinct portal for the recognition and translocation of a large subset of Plasmodium export element effector proteins into the ER, thereby remodelling the infected erythrocyte that is required for parasite survival and pathogenesis.

Repair after damage is essential for tissue homeostasis. Postmenstrual endometrial repair is a cyclical manifestation of rapid, scar-free, tissue repair taking ∼3-5 d. Skin repair after wounding is slower (∼2 wk). In the case of chronic wounds, it takes months to years to restore integrity. Herein, the unique "rapid-repair" endometrial environment is translated to the "slower repair" skin environment. Menstrual fluid (MF), the milieu of postmenstrual endometrial repair, facilitates healing of endometrial and keratinocyte "wounds" in vitro, promoting cellular adhesion and migration, stimulates keratinocyte migration in an ex vivo human skin reconstruct model, and promotes re-epithelialization in an in vivo porcine wound model. Proteomic analysis of MF identified a large number of proteins: migration inhibitory factor, neutrophil gelatinase-associated lipocalin, follistatin like-1, chemokine ligand-20, and secretory leukocyte protease inhibitor were selected for further investigation. Functionally, they promote repair of endometrial and keratinocyte wounds by promoting migration. Translation of these and other MF factors into a migration-inducing treatment paradigm could provide novel treatments for tissue repair.-Evans, J., Infusini, G., McGovern, J., Cuttle, L., Webb, A., Nebl, T., Milla, L., Kimble, R., Kempf, M., Andrews, C. J., Leavesley, D., Salamonsen, L. A. Menstrual fluid factors facilitate tissue repair: identification and functional action in endometrial and skin repair.

Cyanuric acid is a metabolic intermediate of s-triazines, such as atrazine (a common herbicide) and melamine (used in resins and plastics). Cyanuric acid is mineralized to ammonia and carbon dioxide by the soil bacterium Pseudomonas sp. strain ADP via three hydrolytic enzymes (AtzD, AtzE, and AtzF). Here, we report the purification and biochemical and structural characterization of AtzE. Contrary to previous reports, we found that AtzE is not a biuret amidohydrolase, but instead it catalyzes the hydrolytic deamination of 1-carboxybiuret. X-ray crystal structures of apo AtzE and AtzE bound with the suicide inhibitor phenyl phosphorodiamidate revealed that the AtzE enzyme complex consists of two independent molecules in the asymmetric unit. We also show that AtzE forms an α2β2 heterotetramer with a previously unidentified 68-amino acid-long protein (AtzG) encoded in the cyanuric acid mineralization operon from Pseudomonas sp. strain ADP. Moreover, we observed that AtzG is essential for the production of soluble, active AtzE and that this obligate interaction is a vestige of their shared evolutionary origin. We propose that AtzEG was likely recruited into the cyanuric acid-mineralizing pathway from an ancestral glutamine transamidosome that required protein-protein interactions to enforce the exclusion of solvent from the transamidation reaction.

Plasmodium falciparum parasites in the merozoite stage invade human erythrocytes and cause malaria. Invasion requires multiple interactions between merozoite ligands and erythrocyte receptors. P. falciparum reticulocyte binding homolog 5 (PfRh5) forms a complex with the PfRh5-interacting protein (PfRipr) and Cysteine-rich protective antigen (CyRPA) and binds erythrocytes via the host receptor basigin. However, the specific role that PfRipr and CyRPA play during invasion is unclear. Using P. falciparum lines conditionally expressing PfRipr and CyRPA, we show that loss of PfRipr or CyRPA function blocks growth due to the inability of merozoites to invade erythrocytes. Super-resolution microscopy revealed that PfRipr, CyRPA, and PfRh5 colocalize at the junction between merozoites and erythrocytes during invasion. PfRipr, CyRPA, and PfRipr/CyRPA/PfRh5-basigin complex is required for triggering the Ca(2+) release and establishing the tight junction. Together, these results establish that the PfRh5/PfRipr/CyRPA complex is essential in the sequential molecular events leading to parasite invasion of human erythrocytes.

Many insights regarding the pathogenesis of human influenza A virus (IAV) infections have come from studies in mice and ferrets. Surfactant protein (SP)-D is the major neutralizing inhibitor of IAV in mouse airway fluids and SP-D-resistant IAV mutants show enhanced virus replication and virulence in mice. Herein, we demonstrate that sialylated glycoproteins, rather than SP-D, represent the major neutralizing inhibitors against H3 subtype viruses in airway fluids from naïve ferrets. Moreover, while resistance to neutralizing inhibitors is a critical factor in modulating virus replication and disease in the mouse model, it does not appear to be so in the ferret model, as H3 mutants resistant to either SP-D or sialylated glycoproteins in ferret airway fluids did not show enhanced virulence in ferrets. These data have important implications for our understanding of pathogenesis and immunity to human IAV infections in these two widely used animal models of infection.

The Plasmodium translocon for exported proteins (PTEX) has been established as the machinery responsible for the translocation of all classes of exported proteins beyond the parasitophorous vacuolar membrane of the intraerythrocytic malaria parasite. Protein export, particularly in the asexual blood stage, is crucial for parasite survival as exported proteins are involved in remodelling the host cell, an essential process for nutrient uptake, waste removal and immune evasion. Here, we have truncated the conserved C-terminus of one of the essential PTEX components, PTEX150, in Plasmodium falciparum in an attempt to create mutants of reduced functionality. Parasites tolerated C-terminal truncations of up to 125 amino acids with no reduction in growth, protein export or the establishment of new permeability pathways. Quantitative proteomic approaches however revealed a decrease in other PTEX subunits associating with PTEX150 in truncation mutants, suggesting a role for the C-terminus of PTEX150 in regulating PTEX stability. Our analyses also reveal three previously unreported PTEX-associated proteins, namely PV1, Pf113 and Hsp70-x (respective PlasmoDB numbers; PF3D7_1129100, PF3D7_1420700 and PF3D7_0831700) and demonstrate that core PTEX proteins exist in various distinct multimeric forms outside the major complex.

Plasmodium falciparum exports proteins into erythrocytes using the Plasmodium export element (PEXEL) motif, which is cleaved in the endoplasmic reticulum (ER) by plasmepsin V (PMV). A recent study reported that phosphatidylinositol-3-phosphate (PI(3)P) concentrated in the ER binds to PEXEL motifs and is required for export independent of PMV, and that PEXEL motifs are functionally interchangeable with RxLR motifs of oomycete effectors. Here we show that the PEXEL does not bind PI(3)P, and that this lipid is not concentrated in the ER. We find that RxLR motifs cannot mediate export in P. falciparum. Parasites expressing a mutated version of KAHRP, with the PEXEL motif repositioned near the signal sequence, prevented PMV cleavage. This mutant possessed the putative PI(3)P-binding residues but is not exported. Reinstatement of PEXEL to its original location restores processing by PMV and export. These results challenge the PI(3)P hypothesis and provide evidence that PEXEL position is conserved for co-translational processing and export., Export of Plasmodium falciparum proteins into infected erythrocytes relies upon the PEXEL motif in target proteins. Here Boddey et al. challenge the hypothesis that the PEXEL motif mediates export by binding PI(3)P and instead suggest it acts via cleavage by plasmepsin V.

The introduction of manmade chemicals, including the herbicide atrazine, into the environment has led to the emergence of microorganisms with new biodegradation pathways. Esquirol et al. demonstrate that the AtzE enzyme catalyzes a central step in atrazine degradation and that expression of AtzE requires coexpression of the small protein AtzG. Remarkably, AtzG and AtzE appear to have evolved from GatC and GatA, components of an ancient enzyme involved in indirect tRNA aminoacylation, providing an elegant demonstration of metabolic repurposing.

Plasmepsin V, an essential aspartyl protease of malaria parasites, has a key role in the export of effector proteins to parasite-infected erythrocytes. Consequently, it is an important drug target for the two most virulent malaria parasites of humans, Plasmodium falciparum and Plasmodium vivax. We developed a potent inhibitor of plasmepsin V, called WEHI-842, which directly mimics the Plasmodium export element (PEXEL). WEHI-842 inhibits recombinant plasmepsin V with a half-maximal inhibitory concentration of 0.2 nM, efficiently blocks protein export and inhibits parasite growth. We obtained the structure of P. vivax plasmepsin V in complex with WEHI-842 to 2.4-Å resolution, which provides an explanation for the strict requirements for substrate and inhibitor binding. The structure characterizes both a plant-like fold and a malaria-specific helix-turn-helix motif that are likely to be important in cleavage of effector substrates for export.

Neutrophil extracellular traps (NETs) and the cell death associated with it (NETosis) have been implicated in numerous diseases. Mechanistic studies of NETosis have typically relied on nonphysiological stimuli, such as PMA. The human disease of gout is caused by monosodium urate (MSU) crystals. We observed that DNA consistent with NETs is present in fluid from acutely inflamed joints of gout patients. NETs also coat the crystals found in uninflamed tophi of chronic gout patients. We developed a quantitative, live cell imaging assay, which measures the key features of NETosis, namely, cell death and chromatin decondensation. We show that MSU and other physiologically relevant crystals induce NETosis through a molecular pathway that is distinct from PMA and Candida hyphae. Crystals interact with lysosomes to induce NADPH oxidase-independent cell death, with postmortem chromatin decondensation mediated by neutrophil elastase. The resulting MSU-induced NETs are enriched for actin and are resistant to serum and DNase degradation. These findings demonstrate a distinct physiological NETosis pathway in response to MSU crystals, which coats MSU crystals in DNA that persists in tissues as gouty tophi.

The pathogenic nature of malaria infections is due in part to the export of hundreds of effector proteins that actively remodel the host erythrocyte. The Plasmodium translocon of exported proteins (PTEX) has been shown to facilitate the trafficking of proteins into the host cell, a process that is essential for the survival of the parasite. The role of the auxiliary PTEX component PTEX88 remains unclear, as previous attempts to elucidate its function through reverse genetic approaches showed that in contrast to the core components PTEX150 and HSP101, knockdown of PTEX88 did not give rise to an export phenotype. Here, we have used biochemical approaches to understand how PTEX88 assembles within the translocation machinery. Proteomic analysis of the PTEX88 interactome showed that PTEX88 interacts closely with HSP101 but has a weaker affinity with the other core constituents of PTEX. PTEX88 was also found to associate with other PV-resident proteins, including chaperones and members of the exported protein-interacting complex that interacts with the major virulence factor PfEMP1, the latter contributing to cytoadherence and parasite virulence. Despite being expressed for the duration of the blood-stage life cycle, PTEX88 was only discretely observed at the parasitophorous vacuole membrane during ring stages and could not always be detected in the major high molecular weight complex that contains the other core components of PTEX, suggesting that its interaction with the PTEX complex may be dynamic. Together, these data have enabled the generation of an updated model of PTEX that now includes how PTEX88 assembles within the complex.

The most lethal form of malaria in humans is caused by Plasmodium falciparum. These parasites invade erythrocytes, a complex process involving multiple ligand-receptor interactions. The parasite makes initial contact with the erythrocyte followed by dramatic deformations linked to the function of the Erythrocyte binding antigen family and P. falciparum reticulocyte binding-like families. We show EBA-175 mediates substantial changes in the deformability of erythrocytes by binding to glycophorin A and activating a phosphorylation cascade that includes erythrocyte cytoskeletal proteins resulting in changes in the viscoelastic properties of the host cell. TRPM7 kinase inhibitors FTY720 and waixenicin A block the changes in the deformability of erythrocytes and inhibit merozoite invasion by directly inhibiting the phosphorylation cascade. Therefore, binding of P. falciparum parasites to the erythrocyte directly activate a signaling pathway through a phosphorylation cascade and this alters the viscoelastic properties of the host membrane conditioning it for successful invasion. DOI: http://dx.doi.org/10.7554/eLife.21083.001

Malaria is caused by five different Plasmodium spp. in humans each of which modifies the host erythrocyte to survive and replicate. The two main causes of malaria, P. falciparum and P. vivax, differ in their ability to cause severe disease, mainly due to differences in the cytoadhesion of infected erythrocytes (IE) in the microvasculature. Cytoadhesion of P. falciparum in the brain leads to a large number of deaths each year and is a consequence of exported parasite proteins, some of which modify the erythrocyte cytoskeleton while others such as PfEMP1 project onto the erythrocyte surface where they bind to endothelial cells. Here we investigate the effects of knocking out an exported Hsp70-type chaperone termed Hsp70-x that is present in P. falciparum but not P. vivax. Although the growth of Δhsp70-x parasites was unaffected, the export of PfEMP1 cytoadherence proteins was delayed and Δhsp70-x IE had reduced adhesion. The Δhsp70-x IE were also more rigid than wild-type controls indicating changes in the way the parasites modified their host erythrocyte. To investigate the cause of this, transcriptional and translational changes in exported and chaperone proteins were monitored and some changes were observed. We propose that PfHsp70-x is not essential for survival in vitro, but may be required for the efficient export and functioning of some P. falciparum exported proteins.

Establishment of endometrial receptivity is vital for successful embryo implantation. Proprotein convertase 5/6 (referred to as PC6) is up-regulated in the human endometrium specifically at the time of epithelial receptivity. PC6, a serine protease of the proprotein convertase family, plays an important role in converting precursor proteins into their active forms through specific proteolysis. The proform of platelet-derived growth factor A (pro-PDGFA) requires PC cleavage to convert to the active-PDGFA. We investigated the PC6-mediated activation of PDGFA in the human endometrium during the establishment of receptivity. Proteomic analysis identified that the pro-PDGFA was increased in the conditioned medium of HEC1A cells in which PC6 was stably knocked down by small interfering RNA (PC6-siRNA). Western blot analysis demonstrated an accumulation of the pro-PDGFA but a reduction in the active-PDGFA in PC6-siRNA cell lysates and medium compared with control. PC6 cleavage of pro-PDGFA was further confirmed in vitro by incubation of recombinant pro-PDGFA with PC6. Immunohistochemistry revealed cycle-stage-specific localization of the active-PDGFA in the human endometrium. During the non-receptive phase, the active-PDGFA was barely detectable. In contrast, it was localized specifically to the apical surface of the luminal and glandular epithelium in the receptive phase. Furthermore, the active-PDGFA was detected in uterine lavage with levels being significantly higher in the receptive than the non-receptive phase. We thus identified that the secreted PDGFA may serve as a biomarker for endometrial receptivity. This is also the first study demonstrating that the active-PDGFA localizes to the apical surface of the endometrium during receptivity.

Breads prepared from cereal grains are a dietary staple, providing a significant proportion of daily energy, but not necessarily of dietary protein. However, good digestibility of proteins in bread is important to avoid potential immunogenic effects of undigested peptides, including for those gluten-intolerant. Four gluten-containing (white wheat, wholemeal wheat, spelt and rye) and four gluten-free (chick pea, lupin, buckwheat, amaranth) flours were used to make yeast-leavened breads standardized for protein. In vitro gastro-intestinal digestion of pre-mixes, doughs and breads baked for 20 and 35min was conducted followed by correlation analysis between fitted parameters of digestion profiles, chemical composition (protein, non-fibre carbohydrates, fibre, ash and total polyphenolics) and amino acid profiles. The results indicated that digestibility generally increased during proofing and decreased during baking. Relatively higher protein digestibility was correlated with ratio of non-fibre carbohydrate to protein and lower digestibility with increasing contents of fibre and total polyphenolics in pre-mixes.

Human digestion involves chemical, biochemical and fermentative processes integrated to achieve optimal nutrient absorption along the gastro-intestinal (GI) tract. In particular, efficient gastro-intestinal enzymatic digestion of proteins is critical for maximum upper intestinal protein absorption and may influence the distribution of dietary protein between the ‘host’ and microbiota. However, the relative efficiency of infant versus adult conditions of GI digestion of cow’s milk products have not been systematically studied. Conditions for in vitro GI enzymatic digestion, optimised for either infant or adult conditions, were applied to test pasteurised, skimmed milk, skimmed milk powder (SMP) and whey and casein protein fractions of cow’s milk. Research methods included digestion monitoring by o-phthaldialdehyde (OPA) derivitisation of peptides and free amino acids, and digestate analysis to characterise low mass ‘absorbing’ products (size exclusion chromatography) and larger non-absorbing products (700-3500 Da) by MALDI-TOF-MS. The results demonstrated significantly lower digestion efficiency for infant versus adult digestion conditions, particularly in the gastric phase. Digestibility of pasteurised milk and SMP were generally lower than either whey or casein protein fractions. Lower overall protein digestibility was associated with lower and higher proportions of ‘absorbing’ and ‘non-absorbing’ peptides, respectively. The higher yield of ‘non-absorbing’ peptides for infant digestion may permit strategic release of peptides with receptor-antagonistic bioactivity along the gut, and/or may promote supply of nitrogen for the microbiota. The favouring of digestion-resistant peptides to the colon due to processing requires further research to also investigate potential negative relationships with health.

The Plasmodium translocon for exported proteins (PTEX) has been established as the machinery responsible for the translocation of all classes of exported proteins beyond the parasitophorous vacuolar membrane of the intraerythrocytic malaria parasite. Protein export, particularly in the asexual blood stage, is crucial for parasite survival as exported proteins are involved in remodelling the host cell, an essential process for nutrient uptake, waste removal and immune evasion. Here, we have truncated the conserved C-terminus of one of the essential PTEX components, PTEX150, in Plasmodium falciparum in an attempt to create mutants of reduced functionality. Parasites tolerated C-terminal truncations of up to 125 amino acids with no reduction in growth, protein export or the establishment of new permeability pathways. Quantitative proteomic approaches however revealed a decrease in other PTEX subunits associating with PTEX150 in truncation mutants, suggesting a role for the C-terminus of PTEX150 in regulating PTEX stability. Our analyses also reveal three previously unreported PTEX-associated proteins, namely PV1, Pf113 and Hsp70-x (respective PlasmoDB numbers; PF3D7_1129100, PF3D7_1420700 and PF3D7_0831700) and demonstrate that core PTEX proteins exist in various distinct multimeric forms outside the major complex.