Acta crystallographica. Section F, Structural biology communications最新文献

Periodontal diseases afflict 20-50% of the global population and carry serious health and economic burdens. Chronic periodontitis is characterized by inflammation of the periodontal pocket caused by dysbiosis. This dysbiosis is coupled with an increase in the population of Treponema denticola, a spirochete bacterium with high mobility and invasivity mediated by a number of virulence factors. One such virulence factor is TDE0362, a multidomain protein with a carboxy-terminal papain-superfamily cysteine protease (C0362). Most papain-superfamily cysteine proteases are produced as proenzymes with a prodomain that interacts with the prosegment binding loop (PBL), requiring proteolytic processing for full activation. Previous studies have indicated that C0362 is not produced as a proenzyme, suggesting an alternative regulatory mechanism. We previously determined the crystal structure of C0362 captured in an inactive conformation with an oxidized catalytic cysteine and a disordered PBL. In this follow-up study, we evaluated the active-site architecture and the PBL in two mutant (Y559A and C412S) structures and an inhibitor-bound (E64) structure to provide insight into the role that the PBL plays in the generation of active enzyme. Our results implicate Tyr559 as playing a critical role in the transition of the enzyme to an active state. We subsequently utilized the structural information to generate models of C0362 bound to human complement factors C3 and C4. Collectively, our results provide insight into the regulatory mechanism and putative substrate-binding interfaces of C0362, highlighting avenues of further research towards inhibition of this essential virulence factor.

Hen egg-white lysozyme (HEWL) is a small polycationic protein which is highly soluble and stable. This has led to it becoming a `molecular laboratory' where chemical biological operations and structural techniques are tested. To date, HEWL accounts for 1233 PDB entries, roughly 0.5% of the total, making it the best-represented protein in the PDB. With the aim of unambiguously identifying the N atom of the His15 side chain that is most reactive towards iodoacetamide, the structure of chemically modified HEWL was determined by crystallizing it using the `15 minutes lysozyme' protocol. This protocol invariably yields tetragonal crystals of the unmodified protein. To our surprise, we found that the crystals of the modified protein had similar unit-cell parameters but that refinement was only possible when considering an orthorhombic system.

The bacterial enzyme tRNA 2-selenouridine synthase (SelU) catalyzes the conversion of 5-substituted 2-thiouridine (R5S2U) to 5-substituted 2-selenouridine (R5Se2U) at the wobble positions of several tRNAs. Seleno-modification potentially regulates translation efficiency in response to selenium availability. Notably, SelU uses the 2-geranylthiouridine (R5geS2U) intermediate for sulfur removal, and this geranylthiol (geS) is a unique leaving group among tRNA-maturation enzymes. However, the underlying sequence of the SelU reaction remains unclear. Here, a crystallographic study of the Escherichia coli SelU-tRNA complex is reported. Robust and well formed SelU-tRNA crystals were obtained after several optimizations, including co-expression with tRNA and additive screening. Diffraction data were collected at a resolution of 3.10 Å using a wavelength of 1.0000 Å. The crystals belonged to space group C2, and the phase was determined by molecular replacement using the AlphaFold2-predicted SelU structure as a search model. Electron-density mapping revealed the presence of two SelU-tRNA complexes in the asymmetric unit.

X-ray crystallography remains the dominant method of determining the three-dimensional structure of proteins. Nevertheless, this resource-intensive process may be hindered by the unintended crystallization of contaminant proteins from the expression source. Here, the serendipitous discovery of two novel crystal forms and one new, high-resolution structure of carbonic anhydrase 2 (CA2) from Escherichia coli that arose during a crystallization campaign for an unrelated target is reported. By comparing unit-cell parameters with those in the PDB, contaminants such as CA2 can be identified, preventing futile molecular-replacement attempts. Crystallographers can use these new lattice parameters to diagnose CA2 contamination in similar experiments.

Screening of cryo-EM samples is essential for the generation of high-resolution cryo-EM structures. Often, it is cumbersome to correlate the appearance of specific grid squares and micrograph quality. Here, CryoCrane (Correlate atlas and exposures), a visualization tool for cryo-EM screening data, is presented. It aims to provide an intuitive way to visualize micrographs and to speed up data analysis.

Plasmodium vivax, a significant contributor to global malaria cases, poses an escalating health burden on a substantial portion of the world's population. The increasing spread of P. vivax because of climate change underscores the development of new and rational drug-discovery approaches. The Seattle Structural Genomics Center for Infectious Diseases is taking a structure-based approach by investigating essential enzymes such as N-myristoyltransferase (NMT). P. vivax N-myristoyltransferase (PvNMT) is a promising target for the development of novel malaria treatments unlike current drugs, which target only the erythrocytic stages of the parasite. Here, the 1.8 Å resolution ternary structure of PvNMT in complex with myristoyl-CoA and IMP-1088, a validated NMT inhibitor, is reported. IMP-1088 is a validated nonpeptidic inhibitor and a ternary complex structure with human NMT has previously been reported. IMP-1088 binds similarly to PvNMT as to human NMT.

Fenoxaprop-P-ethyl (FE) is widely applied as a post-emergence aryloxyphenoxy propionate (AOPP) herbicide in agriculture. A novel FE hydrolase esterase from Acinetobacter sp. DL-2 (AfeH) was identified which belongs to the family IV carboxylesterases and shows less than 30% identity to other reported homologues with known structure. In order to understand the catalytic mechanism, recombinant AfeH was prepared in Escherichia coli and crystallized using the sitting-drop vapor-diffusion method. X-ray diffraction data were collected to 1.9 Å resolution. The crystal belonged to space group P12₁1, with unit-cell parameters a = 84.27, b = 46.74, c = 258.68 Å. The Matthews coefficient (V_M) was calculated to be 2.43 ų Da^-1, which corresponds to a solvent content of 49.4%, suggesting the presence of three monomers in the crystallographic asymmetric unit. The crystal was assessed to be suitable for further structural determination, which is currently in progress.

Monoclonal antibodies recognizing nonprotein antigens remain largely underrepresented in our understanding of the molecular repertoire of innate and adaptive immunity. One such antibody is Mannitou, a murine IgM that recognizes paucimannosidic glycans. In this work, we report the production and purification of the recombinant antigen-binding fragment (Fab) of Mannitou IgM (Mannitou Fab) and employ a combination of biochemical and biophysical approaches to obtain its initial structural characterization. To this end, recombinant Mannitou Fab comprising the light chain (VL-CL) and heavy chain (VH-Cμ1) was produced in HEK293 FreeStyle cells and purified by cobalt-affinity chromatography followed by size-exclusion chromatography (SEC), which revealed two distinct oligomeric states consistent with a predominant monomeric form and a minor dimeric form. We employed SEC inline with multi-angle light scattering (SEC-MALS) and SEC coupled to small-angle X-ray scattering (SEC-SAXS) to establish that Mannitou Fab indeed adopts monomeric and dimeric forms in solution. Interestingly, Mannitou Fab is N-glycosylated at Asn164 of the heavy chain via HexNAc(5)Hex(6)Fuc(1-3) as revealed by mass spectrometry. We leveraged this information in conjunction with predicted structures of Mannitou Fab to facilitate the interpretation and modelling of SAXS data, leading to a plausible model for glycosylated Mannitou Fab. Analysis of the two chromatographically isolatable forms of Mannitou Fab using synchrotron-radiation circular dichroism revealed that the heat-denaturated Mannitou Fab monomer shares similar secondary-structural elements with the Mannitou Fab dimer, indicating that the latter may be misfolded. Collectively, the findings of this study will set the stage for future structural studies of Mannitou Fab and contribute to our understanding of possible side products due to misfolding during the production of recombinant Fabs, highlighting the importance of glycosylation in obtaining stable and monodisperse monomeric forms of recombinant Fabs.

Helicobacter pylori, a type 1 carcinogen that causes human gastric ulcers and cancer, is a priority target of the Seattle Structural Genomics Center for Infectious Disease (SSGCID). These efforts include determining the structures of potential H. pylori therapeutic targets. Here, the purification, crystallization and X-ray structure of one such target, H. pylori biotin protein ligase (HpBPL), are reported. HpBPL catalyzes the activation of various biotin-dependent metabolic pathways, including fatty-acid synthesis, gluconeogenesis and amino-acid catabolism, and may facilitate the survival of H. pylori in the high-pH gastric mucosa. HpBPL is a prototypical bacterial biotin protein ligase, despite having less than 35% sequence identity to any reported structure in the Protein Data Bank. A biotinyl-5-ATP molecule sits in a well conserved cavity. HpBPL shares extensive tertiary-structural similarity with Mycobacterium tuberculosis biotin protein ligase (MtBPL), despite having less than 22% sequence identity. The active site of HpBPL is very similar to that of MtBPL and has the necessary residues to bind inhibitors developed for MtBPL.