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The repertory of drugs to fight protozoal diseases such as malaria, Chagas' disease, leishmaniasis, and African trypanosomiasis is woefully inadequate. Now, genome sequencing and structural genomics projects are quickly elucidating new drug targets, providing incredible opportunities for medicinal chemists. Here, we illustrate the power of structure-based drug design in this process by our efforts to selectively block trypanosomal glycolysis.

The crystal structure of the intrinsically active cholera toxin mutant is studied for understanding the structural views of an active form of cholera toxin (CT) or Escherichia coli (LT) and it's toxin active mechanism. A model showing the communication to the active site regarding the activation modifications experienced by CT is proposed.

Mycobacterium tuberculosis is a pathogenic bacterial infectious agent that is responsible for approximately 1.5 million human deaths annually. Current treatment requires the long‐term administration of multiple medicines with substantial side effects. Lack of compliance, together with other factors, has resulted in a worrisome increase in resistance. New treatment options are therefore urgently needed. Here, the crystal structure of methionyl‐tRNA synthetase (MetRS), an enzyme critical for protein biosynthesis and therefore a drug target, in complex with its catalytic intermediate methionyl adenylate is reported. Phenylalanine 292 of the M. tuberculosis enzyme is in an `out' conformation and barely contacts the adenine ring, in contrast to other MetRS structures where ring stacking occurs between the adenine and a protein side‐chain ring in the `in' conformation. A comparison with human cytosolic MetRS reveals substantial differences in the active site as well as regarding the position of the connective peptide subdomain 1 (CP1) near the active site, which bodes well for arriving at selective inhibitors. Comparison with the human mitochondrial enzyme at the amino‐acid sequence level suggests that arriving at inhibitors with higher affinity for the mycobacterial enzyme than for the mitochondrial enzyme might be achievable. [ABSTRACT FROM AUTHOR]

American trypanosomiasis, commonly known as Chagas disease, is a neglected tropical disease caused by the protozoan parasite Trypanosoma cruzi. The chronic form of the infection often causes debilitating morbidity and mortality. However, the current treatment for the disease is typically inadequate owing to drug toxicity and poor efficacy, necessitating a continual effort to discover and develop new antiparasitic therapeutic agents. The structure of T. cruzi histidyl-tRNA synthetase (HisRS), a validated drug target, has previously been reported. Based on this structure and those of human cytosolic HisRS, opportunities for the development of specific inhibitors were identified. Here, efforts are reported to identify small molecules that bind to T. cruzi HisRS through fragment-based crystallographic screening in order to arrive at chemical starting points for the development of specific inhibitors. T. cruzi HisRS was soaked into 68 different cocktails from the Medical Structural Genomics of Pathogenic Protozoa (MSGPP) fragment library and diffraction data were collected to identify bound fragments after soaking. A total of 15 fragments were identified, all bound to the same site on the protein, revealing a fragment-binding hotspot adjacent to the ATP-binding pocket. On the basis of the initial hits, the design of reactive fragments targeting the hotspot which would be simultaneously covalently linked to a cysteine residue present only in trypanosomatid HisRS was initiated. Inhibition of T. cruzi HisRS was observed with the resultant reactive fragments and the anticipated binding mode was confirmed crystallographically. These results form a platform for the development of future generations of selective inhibitors for trypanosomatid HisRS. [ABSTRACT FROM AUTHOR]

Parasitic protozoa cause a range of diseases which threaten billions of human beings. They are responsible for tremendous mortality and morbidity in the least-developed areas of the world. Presented here is an overview of the evolution over the last three to four decades of structure-guided design of inhibitors, leads and drug candidates aiming at targets from parasitic protozoa. Target selection is a crucial and multi-faceted aspect of structure-guided drug design. The major impact of advances in molecular biology, genome sequencing and high-throughput screening is touched upon. The most advanced crystallographic techniques, including XFEL, have already been applied to structure determinations of drug targets from parasitic protozoa. Even cryo-electron microscopy is contributing to our understanding of the mode of binding of inhibitors to parasite ribosomes. A number of projects have been selected to illustrate how structural information has assisted in arriving at promising compounds that are currently being evaluated by pharmacological, pharmacodynamic and safety tests to assess their suitability as pharmaceutical agents. Structure-guided approaches are also applied to incorporate properties into compounds such that they are less likely to become the victim of resistance mechanisms. A great increase in the number of novel antiparasitic compounds will be needed in the future. These should then be combined into various multi-compound therapeutics to circumvent the diverse resistance mechanisms that render single-compound, or even multi-compound, drugs ineffective. The future should also see (i) an increase in the number of projects with a tight integration of structural biology, medicinal chemistry, parasitology and pharmaceutical sciences; (ii) the education of more `medicinal structural biologists' who are familiar with the properties that compounds need to have for a high probability of success in the later steps of the drug-development process; and (iii) the expansion of drug-development capabilities in middle- and low-income countries. [ABSTRACT FROM AUTHOR]

Improved therapies for the treatment of Trypanosoma brucei, the etiological agent of the neglected tropical disease human African trypanosomiasis, are urgently needed. We targeted T. brucei methionyl-tRNA synthetase (MetRS), an aminoacyl-tRNA synthase (aaRS), which is considered an important drug target due to its role in protein synthesis, cell survival, and its significant differences in structure from its mammalian ortholog. Previous work using RNA interference of MetRS demonstrated growth inhibition of T. brucei, further validating it as an attractive target. We report the development and implementation of two orthogonal high-throughput screening assays to identify inhibitors of T. brucei MetRS. First, a chemiluminescence assay was implemented in a 1536-well plate format and used to monitor adenosine triphosphate depletion during the aminoacylation reaction. Hit confirmation then used a counterscreen in which adenosine monophosphate production was assessed using fluorescence polarization technology. In addition, a miniaturized cell viability assay was used to triage cytotoxic compounds. Finally, lower throughput assays involving whole parasite growth inhibition of both human and parasite MetRS were used to analyze compound selectivity and efficacy. The outcome of this high-throughput screening campaign has led to the discovery of 19 potent and selective T. brucei MetRS inhibitors. [ABSTRACT FROM PUBLISHER]

Methionyl-tRNA synthetase of Trypanosoma brucei (TbMetRS) is an important target in the development of new antitrypanosomal drugs. The enzyme is essential, highly flexible and displaying a large degree of changes in protein domains and binding pockets in the presence of substrate, product and inhibitors. Targeting this protein will benefit from a profound understanding of how its structure adapts to ligand binding. A series of urea-based inhibitors (UBIs) has been developed with IC50 values as low as 19 nM against the enzyme. The UBIs were shown to be orally available and permeable through the blood-brain barrier, and are therefore candidates for development of drugs for the treatment of late stage human African trypanosomiasis. Here, we expand the structural diversity of inhibitors from the previously reported collection and tested for their inhibitory effect on TbMetRS and on the growth of T. brucei cells. The binding modes and binding pockets of 14 UBIs are revealed by determination of their crystal structures in complex with TbMetRS at resolutions between 2.2 Å to 2.9 Å. The structures show binding of the UBIs through conformational selection, including occupancy of the enlarged methionine pocket and the auxiliary pocket. General principles underlying the affinity of UBIs for TbMetRS are derived from these structures, in particular the optimum way to fill the two binding pockets. The conserved auxiliary pocket might play a role in binding tRNA. In addition, a crystal structure of a ternary TbMetRS•inhibitor•AMPPCP complex indicates that the UBIs are not competing with ATP for binding, instead are interacting with ATP through hydrogen bond. This suggests a possibility that a general 'ATP-engaging' binding mode can be utilized for the design and development of inhibitors targeting tRNA synthetases of other disease-causing pathogen. Author Summary: Infection by the protozoan parasite Trypanosoma brucei causes sleeping sickness, also called human African trypanosomiasis. Without treatment, the disease is fatal yet current therapeutic options are inadequate and better medicines are needed. We have previously reported several potent inhibitors of T. brucei methionyl-tRNA synthetase, an essential enzyme involved in the protein biosynthesis. Recently, a new series of the inhibitors was synthesized which has improved membrane permeability over the earlier inhibitors. When applied to mouse with T. brucei infection, the new compounds are orally available and reach the central nervous system to reduce parasite loads, and therefore are promising molecules to be developed into antitrypanosomal drug. Here, more inhibitors from this series are reported and tested for their activities. High resolution crystal structures were determined that revealed how these inhibitors bind to the target enzyme. The binding pockets of these inhibitors are thoroughly explored, providing profound insights which are beneficial for further development of MetRS inhibitors against sleeping sickness. A ternary complex of the enzyme, an inhibitor, and an ATP analogue was also determined, indicates that the inhibitor does not compete with ATP for binding. Based on this, a general approach to use inhibitors that engage ATP for binding to tRNA synthetases is proposed. [ABSTRACT FROM AUTHOR]

Methionyl-tRNA synthetase of Trypanosoma brucei (TbMetRS) is an important target in the development of new antitrypanosomal drugs. The enzyme is essential, highly flexible and displaying a large degree of changes in protein domains and binding pockets in the presence of substrate, product and inhibitors. Targeting this protein will benefit from a profound understanding of how its structure adapts to ligand binding. A series of urea-based inhibitors (UBIs) has been developed with IC50 values as low as 19 nM against the enzyme. The UBIs were shown to be orally available and permeable through the blood-brain barrier, and are therefore candidates for development of drugs for the treatment of late stage human African trypanosomiasis. Here, we expand the structural diversity of inhibitors from the previously reported collection and tested for their inhibitory effect on TbMetRS and on the growth of T. brucei cells. The binding modes and binding pockets of 14 UBIs are revealed by determination of their crystal structures in complex with TbMetRS at resolutions between 2.2 Å to 2.9 Å. The structures show binding of the UBIs through conformational selection, including occupancy of the enlarged methionine pocket and the auxiliary pocket. General principles underlying the affinity of UBIs for TbMetRS are derived from these structures, in particular the optimum way to fill the two binding pockets. The conserved auxiliary pocket might play a role in binding tRNA. In addition, a crystal structure of a ternary TbMetRS•inhibitor•AMPPCP complex indicates that the UBIs are not competing with ATP for binding, instead are interacting with ATP through hydrogen bond. This suggests a possibility that a general ‘ATP-engaging’ binding mode can be utilized for the design and development of inhibitors targeting tRNA synthetases of other disease-causing pathogen. [ABSTRACT FROM AUTHOR]

Despite the enormous economic importance of Neospora caninum related veterinary diseases, the number of effective therapeutic agents is relatively small. Development of new therapeutic strategies to combat the economic impact of neosporosis remains an important scientific endeavor. This study demonstrates molecular, structural and phenotypic evidence that N. caninum calcium-dependent protein kinase 1 (NcCDPK1) is a promising molecular target for neosporosis drug development. Recombinant NcCDPK1 was expressed, purified and screened against a select group of bumped kinase inhibitors (BKIs) previously shown to have low IC50s against Toxoplasma gondii CDPK1 and T. gondii tachyzoites. NcCDPK1 was inhibited by low concentrations of BKIs. The three-dimensional structure of NcCDPK1 in complex with BKIs was studied crystallographically. The BKI-NcCDPK1 structures demonstrated the structural basis for potency and selectivity. Calcium-dependent conformational changes in solution as characterized by small-angle X-ray scattering are consistent with previous structures in low Calcium-state but different in the Calcium-bound active state than predicted by X-ray crystallography. BKIs effectively inhibited N. caninum tachyzoite proliferation in vitro. Electron microscopic analysis of N. caninum cells revealed ultra-structural changes in the presence of BKI compound 1294. BKI compound 1294 interfered with an early step in Neospora tachyzoite host cell invasion and egress. Prolonged incubation in the presence of 1294 interfered produced observable interference with viability and replication. Oral dosing of BKI compound 1294 at 50 mg/kg for 5 days in established murine neosporosis resulted in a 10-fold reduced cerebral parasite burden compared to untreated control. Further experiments are needed to determine the PK, optimal dosage, and duration for effective treatment in cattle and dogs, but these data demonstrate proof-of-concept for BKIs, and 1294 specifically, for therapy of bovine and canine neosporosis. [ABSTRACT FROM AUTHOR]

The genome of the human intestinal parasite Giardia lamblia contains only a single aminoacyl-tRNA synthetase gene for each amino acid. The Giardia prolyl-tRNA synthetase gene product was originally misidentified as a dual-specificity Pro/Cys enzyme, in part owing to its unexpectedly high off-target activation of cysteine, but is now believed to be a normal representative of the class of archaeal/eukaryotic prolyl-tRNA synthetases. The 2.2 Å resolution crystal structure of the G. lamblia enzyme presented here is thus the first structure determination of a prolyl-tRNA synthetase from a eukaryote. The relative occupancies of substrate (proline) and product (prolyl-AMP) in the active site are consistent with half-of-the-sites reactivity, as is the observed biphasic thermal denaturation curve for the protein in the presence of proline and MgATP. However, no corresponding induced asymmetry is evident in the structure of the protein. No thermal stabilization is observed in the presence of cysteine and ATP. The implied low affinity for the off-target activation product cysteinyl-AMP suggests that translational fidelity in Giardia is aided by the rapid release of misactivated cysteine. [ABSTRACT FROM AUTHOR]

Many Gram-negative bacteria use the sophisticated type II secretion system (T2SS) to translocate a wide range of proteins from the periplasm across the outer membrane. The inner-membrane platform of the T2SS is the nexus of the system and orchestrates the secretion process through its interactions with the periplasmic filamentous pseudopilus, the dodecameric outer-membrane complex and a cytoplasmic secretion ATPase. Here, recent structural and biochemical information is reviewed to describe our current knowledge of the biogenesis and architecture of the T2SS and its mechanism of action. [ABSTRACT FROM AUTHOR]

Type II secretion systems (T2SSs) are critical for secretion of many proteins from Gram-negative bacteria. In the T2SS, the outer membrane secretin GspD forms a multimeric pore for translocation of secreted proteins. GspD and the inner membrane protein GspC interact with each other via periplasmic domains. Three different crystal structures of the homology region domain of GspC (GspCHR) in complex with either two or three domains of the N-terminal region of GspD from enterotoxigenic Escherichia coli show that GspCHR adopts an all-β topology. N-terminal β-strands of GspC and the N0 domain of GspD are major components of the interface between these inner and outer membrane proteins from the T2SS. The biological relevance of the observed GspC-GspD interface is shown by analysis of variant proteins in two-hybrid studies and by the effect of mutations in homologous genes on extracellular secretion and subcellular distribution of GspC in Vibrio cholerae. Substitutions of interface residues of GspD have a dramatic effect on the focal distribution of GspC in V. cholerae. These studies indicate that the GspCHR--GspDN0 interactions observed in the crystal structure are essential for T2SS function. Possible implications of our structures for the stoichiometry of the T2SS and exoprotein secretion are discussed. [ABSTRACT FROM AUTHOR]

The type II secretion system (T2SS) is a macromolecular complex spanning the inner and outer membranes of Gram-negative bacteria. Remarkably, the T2SS secretes folded proteins, including multimeric assemblies such as cholera toxin and heat-labile enterotoxin from Vibrio cholerae and enterotoxigenic Escherichia coli, respectively. The major outer membrane T2SS protein is the 'secretin' GspD. Cryo-EM reconstruction of the V. cholerae secretin at 19-Å resolution reveals a dodecameric structure reminiscent of a barrel, with a large channel at its center that contains a closed periplasmic gate. The GspD periplasmic domain forms a vestibule with a conserved constriction, and it binds to a pentameric exoprotein and to the trimeric tip of the T2SS pseudopilus. By combining our results with structures of the cholera toxin and T2SS pseudopilus tip, we provide a structural basis for a possible secretion mechanism of the T2SS. [ABSTRACT FROM AUTHOR]

New drugs are needed to treat toxoplasmosis. Toxoplasma gondii calcium-dependent protein kinases (TgCDPKs) are attractive targets because they are absent in mammals. We show that TgCDPK1 is inhibited by low nanomolar levels of bumped kinase inhibitors (BKIs), compounds inactive against mammalian kinases. Cocrystal structures of TgCDPK1 with BKIs confirm that the structural basis for selectivity is due to the unique glycine gatekeeper residue in the ATP-binding site. We show that BKIs interfere with an early step in T. gondii infection of human cells in culture. Furthermore, we show that TgCDPK1 is the in vivo target of BKIs because T. gondii expressing a glycine to methionine gatekeeper mutant enzyme show significantly decreased sensitivity to BKIs. Thus, design of selective TgCDPK1 inhibitors with low host toxicity may be achievable. [ABSTRACT FROM AUTHOR]

The article presents a study that investigates the efforts of the medical structural genomics in the discovery of new drugs for infectious diseases. It offers information on medical structural genomics particularly on the structures of medically relevant drug targets in pathogens that serves as a starting point for inhibitor design and drug development. A chart is presented depicting the protein structure information in the design and development of new therapeutic entities.

In the past decade, thermal melt/thermal shift assays have become a common tool for identifying ligands and other factors that stabilize specific proteins. Increased stability is indicated by an increase in the protein's melting temperature (Tm). In optimizing the assays for subsequent screening of compound libraries, it is important to minimize the variability of Tm measurements so as to maximize the assay's ability to detect potential ligands. The authors present an investigation of Tm variability in recombinant proteins from Plasmodium parasites. Ligands of Plasmodium proteins are particularly interesting as potential starting points for drugs for malaria, and new drugs are urgently needed. A single standard buffer (100 mM HEPES [pH 7.5], 150 mM NaCl) permitted estimation of Tm for 58 of 61 Plasmodium proteins tested. However, with several proteins, Tm could not be measured with a consistency suitable for high-throughput screening unless alternative protein-specific buffers were employed. The authors conclude that buffer optimization to minimize variability in Tm measurements increases the success of thermal melt screens involving proteins for which a standard buffer is suboptimal. [ABSTRACT FROM AUTHOR]

Gram-negative bacteria translocate various proteins including virulence factors across their outer membrane via type 2 secretion systems (T2SSs). T2SSs are thought to contain a pseudopilus, a subcomplex formed by one major and several minor pseudopilins. We report the crystal structure of the complex formed by three minor pseudopilins from enterotoxigenic Escherichia coli. The GspK–GspI–GspJ complex has quasihelical characteristics and an architecture consistent with a localization at the pseudopilus tip. The α-domain of GspK has a previously unobserved fold with an unexpected dinuclear metal binding site. The area surrounding its disulfide bridge is conserved and might interact with other T2SS components or with secreted proteins. [ABSTRACT FROM AUTHOR]

An actomyosin motor located underneath the plasma membrane drives motility and host-cell invasion of apicomplexan parasites such as Plasmodium falciparum and Plasmodium vivax, the causative agents of malaria. Aldolase connects the motor actin filaments to transmembrane adhesive proteins of the thrombospondin-related anonymous protein (TRAP) family and transduces the motor force across the parasite surface. The TRAP-aldolase interaction is a distinctive and critical trait of host hepatocyte invasion by Plasmodium sporozoites, with a likely similar interaction crucial for erythrocyte invasion by merozoites. Here, we describe 2.4-Å and 2.7-Å structures of P. falciparum aldolase (PfAldo) obtained from crystals grown in the presence of the C-terminal hexapeptide of TRAP from Plasmodium berghei. The indole ring of the critical penultimate Trp-residue of TRAP fits snugly into a newly formed hydrophobic pocket, which is exclusively delimited by hydrophilic residues: two arginines, one glutamate, and one glutamine. Comparison with the unliganded PfAldo structure shows that the two arginines adopt new side-chain rotamers, whereas a 25-residue subdomain, forming a helix-loop-helix unit, shifts upon binding the TRAP-tail. The structural data are in agreement with decreased TRAP binding after mutagenesis of PfAldo residues in and near the induced TRAP-binding pocket. Remarkably, the TRAP- and actin-binding sites of PfAldo seem to overlap, suggesting that both the plasticity of the aldolase active-site region and the multimeric nature of the enzyme are crucial for its intriguing nonenzymatic function in the invasion machinery of the malaria parasite. [ABSTRACT FROM AUTHOR]

The structure of a putative Raf kinase inhibitor protein (RKIP) homolog from the eukaryotic parasite Plasmodium vivax has been studied to a resolution of 1.3 Å using multiple-wavelength anomalous diffraction at the Se K edge. This protozoan protein is topologically similar to previously studied members of the phosphatidylethanolamine-binding protein (PEBP) sequence family, but exhibits a distinctive left-handed α-helical region at one side of the canonical phospholipid-binding site. Re-examination of previously determined PEBP structures suggests that the P. vivax protein and yeast carboxypeptidase Y inhibitor may represent a structurally distinct subfamily of the diverse PEBP-sequence family. [ABSTRACT FROM AUTHOR]

A complex molecular motor empowers substrate-dependent motility and host cell invasion in malaria parasites. The interaction between aldolase and the transmembrane adhesin thrombospondin-related anonymous protein (TRAP) transduces the motor force across the parasite surface. Here, we analyzed this interaction by using state-of-the-art flexible docking. Besides algorithms to account for induced fit in the side-chains of the Plasmodium falciparum aldolase (PfAldo) structure, we used additional in silico receptors modeled upon crystallographic structures of evolutionarily related aldolases to incorporate enzyme backbone flexibility, and to overcome structure inaccuracies due to the relatively low resolution (3.0 Å) of the genuine PfAldo structure. Our results indicate that, in spite of multiple intermolecular contacts, only the six C-terminal residues of the TRAP cytoplasmic tail bind in an ordered manner to PfAldo. This portion of TRAP targets the PfAldo active site, with its n-1 Trp residue, which is essential for this interaction, buried within the PfAldo catalytic pocket. Docking of a TRAP peptide bearing a Trp to Ala mutation rendered the lower energy configurations either bound weakly outside the active site or not bound to PfAldo at all. The position of the bound TRAP peptide, and particularly the close proximity between the carbonyl of its n-2 Asp residue and the experimentally determined position of the phosphate-6 group of fructose 1,6-phosphate bound to mammalian aldolases, predicts an inhibitory effect of TRAP on catalysis. Enzymatic and TRAP-binding assays using mutant PfAldo molecules strongly support the overall structural model. These results might provide the initial framework for the identification of novel antiparasitic compounds. Proteins 2007. © 2006 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

EpsE is a cytoplasmic component of the type II secretion system in Vibrio cholerae. Through ATP hydrolysis and an interaction with the cytoplasmic membrane protein EpsL, EpsE supports secretion of cholera toxin across the outer membrane. In this study, we have determined the effect of the cytoplasmic domain of EpsL (cyto-EpsL) and purified phospholipids on the ATPase activity of EpsE. Acidic phospholipids, specifically cardiolipin, bound the copurified EpsE/cyto-EpsL complex and stimulated its ATPase activity 30–130-fold, whereas the activity of EpsE alone was unaffected. Removal of the last 11 residues (residues 243–253) from cyto-EpsL prevented cardiolipin binding as well as stimulation of the ATPase activity of EpsE. Further mutagenesis of the C-terminal region of the EpsL cytoplasmic domain adjacent to the predicted transmembrane helix suggested that this region participates in fine tuning the interaction of EpsE with the cytoplasmic membrane and influences the oligomerization state of EpsE thereby stimulating its ATPase activity and promoting extracellular secretion in V. cholerae. [ABSTRACT FROM AUTHOR]

The structure of ribose 5-phosphate isomerase from Plasmodium falciparum, PFE0730c, has been determined by molecular replacement at 2.09 Å resolution. The enzyme, which catalyzes the isomerization reaction that interconverts ribose 5-phosphate and ribulose 5-phosphate, is a member of the pentose phosphate pathway. The P. falciparum enzyme belongs to the ribose 5-­phosphate isomerase A family, Pfam family PF06562 (DUF1124), and is structurally similar to other members of the family. [ABSTRACT FROM AUTHOR]

The structure of a conserved hypothetical protein, PlasmoDB sequence MAL13P1.257 from Plasmodium falciparum, Pfam sequence family PF05907, has been determined as part of the structural genomics effort of the Structural Genomics of Pathogenic Protozoa consortium. The structure was determined by multiple-wavelength anomalous dispersion at 2.17 Å resolution. The structure is almost entirely β-sheet; it consists of 15 β-strands and one short 310-helix and represents a new protein fold. The packing of the two monomers in the asymmetric unit indicates that the biological unit may be a dimer. [ABSTRACT FROM AUTHOR]

The gene product of structural genomics target Lmaj006129 from Leishmania major codes for a 164-residue protein of unknown function. When SeMet expression of the full-length gene product failed, several truncation variants were created with the aid of Ginzu, a domain-prediction method. 11 truncations were selected for expression, purification and crystallization based upon secondary-structure elements and disorder. The structure of one of these variants, Lmaj006129AAH, was solved by multiple-wavelength anomalous diffraction (MAD) using ELVES, an automatic protein crystal structure-determination system. This model was then successfully used as a molecular-replacement probe for the parent full-length target, Lmaj006129AAA. The final structure of Lmaj006129AAA was refined to an R value of 0.185 ( Rfree = 0.229) at 1.60 Å resolution. Structure and sequence comparisons based on Lmaj006129AAA suggest that proteins belonging to Pfam sequence families PF04543 and PF01878 may share a common ligand-binding motif. [ABSTRACT FROM AUTHOR]

Gram-negative bacteria use the type II secretion system to transport a large number of secreted proteins from the periplasmic space into the extracellular environment. Many of the secreted proteins are major virulence factors in plants and animals. The components of the type II secretion system are located in both the inner and outer membranes where they assemble into a multi-protein, cell-envelope spanning, complex. This review discusses recent progress, particularly newly published structures obtained by X-ray crystallography and electron microscopy that have increased our understanding of how the type II secretion apparatus functions and the role that individual proteins play in this complex system. [ABSTRACT FROM AUTHOR]

The crystal structure of Pfal009167AAA, a putative ribulose 5-phosphate 3-epimerase (PfalRPE) from Plasmodium falciparum, has been determined to 2 Å resolution. RPE represents an exciting potential drug target for developing antimalarials because it is involved in the shikimate and the pentose phosphate pathways. The structure is a classic TIM-barrel fold. A coordinated Zn ion and a bound sulfate ion in the active site of the enzyme allow for a greater understanding of the mechanism of action of this enzyme. This structure is solved in the framework of the Structural Genomics of Pathogenic Protozoa (SGPP) consortium. Proteins 2006. © 2005 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]