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Thrombospondin type-1 repeats (TSRs) are small protein motifs containing six conserved cysteines forming three disulfide bonds that can be modified with an O-linked fucose. Protein O-fucosyltransferase 2 (POFUT2) catalyzes the addition of O-fucose to TSRs containing the appropriate consensus sequence, and the O-fucose modification can be elongated to a Glucose-Fucose disaccharide with the addition of glucose by ß3-glucosyltransferase (B3GLCT). Elimination of Pofut2 in mice results in embryonic lethality in mice, highlighting the biological significance of O-fucose modification on TSRs. Knockout of POFUT2 in HEK293T cells has been shown to cause complete or partial loss of secretion of many proteins containing O-fucosylated TSRs. In addition, POFUT2 is localized to the endoplasmic reticulum (ER) and only modifies folded TSRs, stabilizing their structures. These observations suggest that POFUT2 is involved in an ER quality control mechanism for TSR folding and that B3GLCT also participates in quality control by providing additional stabilization to TSRs. However, the mechanisms by which addition of these sugars result in stabilization are poorly understood. Here, we conducted molecular dynamics (MD) simulations and provide crystallographic and NMR evidence that the Glucose-Fucose disaccharide interacts with specific amino acids in the TSR3 domain in thrombospondin-1 that are within proximity to the O-fucosylation modification site resulting in protection of a nearby disulfide bond. We also show that mutation of these amino acids reduces the stabilizing effect of the sugars in vitro. These data provide mechanistic details regarding the importance of O-fucosylation and how it participates in quality control mechanisms inside the ER.

10 pags., 3 figs., 2 tabs. -- Open Access funded by Creative Commons Atribution Licence 4.0, Fungal cell wall synthesis is achieved by a balance of glycosyltransferase, hydrolase and transglycosylase activities. Transglycosylases strengthen the cell wall by forming a rigid network of crosslinks through mechanisms that remain to be explored. Here we study the function of the Aspergillus fumigatus family of five Crh transglycosylases. Although crh genes are dispensable for cell viability, simultaneous deletion of all genes renders cells sensitive to cell wall interfering compounds. In vitro biochemical assays and localisation studies demonstrate that this family of enzymes functions redundantly as transglycosylases for both chitin-glucan and chitin-chitin cell wall crosslinks. To understand the molecular basis of this acceptor promiscuity, we solved the crystal structure of A. fumigatus Crh5 (AfCrh5) in complex with a chitooligosaccharide at the resolution of 2.8 Å, revealing an extensive elongated binding cleft for the donor (−4 to −1) substrate and a short acceptor (+1 to +2) binding site. Together with mutagenesis, the structure suggests a “hydrolysis product assisted” molecular mechanism favouring transglycosylation over hydrolysis., We thank the European Synchrotron Radiation Facility beamlines ID29 and ID30A-1, Grenoble, France. This work was funded by MRC Programme Grant (M004139) to D.M.F.v.A., Research Start-up Funding of Guangxi Academy of Sciences (2017YJJ025) and Guangxi Natural Science Foundation (2018GXNSFAA138012) to W.F., ARAID to R.H-G., Ministerio de Economía (MINECO) to both R.H-G. and J.A. (CTQ2013-44367- C2-2-P and BFU2016-75633-P to R.H-G., and BIO2016-79289-P to J.A.), DGA to R.H-G. (E34_R17), and Comunidad de Madrid (FSE, FEDER) (S2017/BMD-3691 InGEMICS-CM) to J.A. A.B.S. was supported by contract from Comunidad de Madrid (FSE, FEDER).

Póster presentado en el 42º SEI, Congreso de la Sociedad Española de Inmunología, formato virtual, 24-26 marzo de 2021, Madrid., Fungal diseases affect annually more than 150 million people and mortality rounds around 1,7 million people. Furthermore, drug resistance among fungal species is steadily increasing during last years, so new treatments for fungal diseases are required. We report a camelid nanobody which shows in vitro inhibitory capabilities against A. fumigatus and C. neoformans β-1,3-glucanosyltransferases and reduces the growth rates of both fungi. This inhibitory nanobody has been tested in C. elegans models of aspergillosis and cryptococcosis, obtaining an improvement in survival rates. Such results led us to verify its effectiveness in murine models of aspergillosis and cryptococcosis, in which similar performance was also obtained. In this way, our findings reveal that inhibitory nanobodies targeted against fungal crucial enzymes can be used as novel antibiotics which may improve therapeutic outcome.

The present invention refers to the treatment of fungal infections or diseases by using specific affinity reagents, such as nanobodies, which specifically bind the fungal β-1,3-glucanosyltransferase gel4., Universidad de Zaragoza, Fundación Agencia Aragonesa para la Investigación y el Desarrollo (ARAID), Universidad Complutense de Madrid, Vrije Universiteit Brussel, Consejo Superior de Investigaciones Científicas, A1 Solicitud de patente con informe sobre el estado de la técnica

The Tn antigen (GalNAc-a-1-O-Thr/Ser) is a well-known tumor-associated carbohydrate determinant. The use of glycopeptides that incorporate this structure has become a significant and promising niche of research owing to their potential use as anticancer vaccines. Herein, the conformational preferences of a glycopeptide with an unnatural Tn antigen, characterized by a threonine decorated with an sp2-iminosugar-type a-GalNAc mimic, have been studied both in solution, by combining NMR spectroscopy and molecular dynamics simulations, and in the solid state bound to an anti-mucin-1 (MUC1) antibody, by X-ray crystallography. The Tn surrogate can mimic the main conformer sampled by the natural antigen in solution and exhibits high affinity towards anti-MUC1 antibodies. Encouraged by these data, a cancer vaccine candidate based on this unnatural glycopeptide and conjugated to the carrier protein Keyhole Limpet Hemocyanin (KLH) has been prepared and tested in mice. Significantly, the experiments in vivo have proved that this vaccine elicits higher levels of specific anti-MUC1 IgG antibodies than the analog that bears the natural Tn antigen and that the elicited antibodies recognize human breast cancer cells with high selectivity. Altogether, we compile evidence to confirm that the presentation of the antigen, both in solution and in the bound state, plays a critical role in the efficacy of the designed cancer vaccines. Moreover, the outcomes derived from this vaccine prove that there is room for exploring further adjustments at the carbohydrate level that could contribute to designing more efficient cancer vaccines.

Trabajo presentado en el III Workshop NanoOncología en Zaragoza, celebrado del 14 al 15 de enero de 2020, en la Facultad de Medicina de la Universidad de Zaragoza.

Mucin-type O-glycosylation is a post-translational modification (PTM) that is predicted to occur in more than the 80% of the proteins that pass through the Golgi apparatus. This PTM is initiated by a family of polypeptide GalNAc-transferases (GalNAc-Ts) that modify Ser and Thr residues of proteins through the addition of a GalNAc moiety. These enzymes are type II membrane proteins that consist of a Golgi luminal catalytic domain connected by a flexible linker to a ricin type lectin domain. Together, both domains account for the different glycosylation preferences observed among isoenzymes. Although it is well accepted that most of the family members share some degree of redundancy toward their protein and glycoprotein substrates, it has been recently found that several GalNAc-Ts also possess activity toward specific targets. Despite the high similarity between isoenzymes, structural differences have recently been reported that are key to understanding the molecular basis of both their redundancy and specificity. The present review focuses on the molecular aspects of the protein substrate recognition and the different glycosylation preferences of these enzymes, which in turn will serve as a roadmap to the rational design of specific modulators of mucin-type O-glycosylation.

The bacterial effector proteins SseK and NleB glycosylate host proteins on arginine residues, leading to reduced NF-kappa B-dependent responses to infection. Salmonella SseK1 and SseK2 are E. coli NleB1 orthologs that behave as NleB1-like GTs, although they differ in protein substrate specificity. Here we report that these enzymes are retaining glycosyltransferases composed of a helix-loop-helix (HLH) domain, a lid domain, and a catalytic domain. A conserved HEN motif (His-Glu-Asn) in the active site is important for enzyme catalysis and bacterial virulence. We observe differences between SseK1 and SseK2 in interactions with substrates and identify substrate residues that are critical for enzyme recognition. Long Molecular Dynamics simulations suggest that the HLH domain determines substrate specificity and the lid-domain regulates the opening of the active site. Overall, our data suggest a front-face S(N)i mechanism, explain differences in activities among these effectors, and have implications for future drug development against enteric pathogens.

Protein O-fucosylation is an important post-translational modification (PTM) found in cysteine-rich repeats in proteins. Protein O-fucosyltransferases 1 and 2 (PoFUT1 and PoFUT2) are the enzymes responsible for this PTM and selectively glycosylate specific residues in epidermal growth factor-like (EGF) repeats and thrombospondin type I repeats (TSRs), respectively.Within the past six years, crystal structures of both enzymes have been reported, revealing important information on how they recognize protein substrates and achieve catalysis. Here, the structural information available today is summarized and how PoFUT1 and PoFUT2 employ different catalytic mechanisms is discussed.

The family of polypeptide N-acetylgalactosamine (GalNAc) transferases (GalNAc-Ts) orchestrates the initiating step of mucin-type protein O-glycosylation by transfer of GalNAc moieties to serine and threonine residues in proteins. Deficiencies and dysregulation of GalNAc-T isoenzymes are related to different diseases. Recently, it has been demonstrated that an inactive GalNAc-T2 mutant (F104S), which is not located at the active site, induces low levels of high-density lipoprotein cholesterol (HDL-C) in humans. Herein, the molecular basis for F104S mutant inactivation has been deciphered. Saturation transfer difference NMR spectroscopy experiments demonstrate that the mutation induces loss of binding to peptide substrates. Analysis of the crystal structure of the F104S mutant bound to UDP-GalNAc (UDP=uridine diphosphate), combined with molecular dynamics (MD) simulations, has revealed that the flexible loop is disordered and displays larger conformational changes in the mutant enzyme than that in the wild-type (WT) enzyme. 19F NMR spectroscopy experiments reveal that the WT enzyme only reaches the active state in the presence of UDP-GalNAc, which provides compelling evidence that GalNAc-T2 adopts a UDP-GalNAc-dependent induced-fit mechanism. The F104S mutation precludes the enzyme from achieving the active conformation and concomitantly binding peptide substrates. This study provides new insights into the catalytic mechanism of the large family of GalNAc-Ts and how these enzymes orchestrate protein O-glycosylation.