Members of the bacterial genus Brucella cause brucellosis, a zoonotic disease that affects both livestock and wildlife. Brucella are category B infectious agents that can be aerosolized for ...biological warfare. As part of the structural genomics studies at the Seattle Structural Genomics Center for Infectious Disease (SSGCID), FolM alternative dihydrofolate reductases 1 from Brucella suis and Brucella canis were produced and their structures are reported. The enzymes share ∼95% sequence identity but have less than 33% sequence identity to other homologues with known structure. The structures are prototypical NADPH‐dependent short‐chain reductases that share their highest tertiary‐structural similarity with protozoan pteridine reductases, which are being investigated for rational therapeutic development.
Crystal structures of FolM alternative dihydrofolate reductase 1 from Brucella suis and Brucella canis reveal prototypical NADPH‐dependent short‐chain reductases with structural similarity to protozoan pteridine reductases that are potential drug targets.
During human infection, Mycobacterium tuberculosis (Mtb) survives the normally bacteriocidal phagosome of macrophages. Mtb and related species may be able to combat this harsh acidic environment ...which contains reactive oxygen species due to the mycobacterial genomes encoding a large number of dehydrogenases. Typically, dehydrogenase cofactor binding sites are open to solvent, which allows NAD/NADH exchange to support multiple turnover. Interestingly, mycobacterial short chain dehydrogenases/reductases (SDRs) within family TIGR03971 contain an insertion at the NAD binding site. Here we present crystal structures of 9 mycobacterial SDRs in which the insertion buries the NAD cofactor except for a small portion of the nicotinamide ring. Line broadening and STD-NMR experiments did not show NAD or NADH exchange on the NMR timescale. STD-NMR demonstrated binding of the potential substrate carveol, the potential product carvone, the inhibitor tricyclazol, and an external redox partner 2,6-dichloroindophenol (DCIP). Therefore, these SDRs appear to contain a non-exchangeable NAD cofactor and may rely on an external redox partner, rather than cofactor exchange, for multiple turnover. Incidentally, these genes always appear in conjunction with the mftA gene, which encodes the short peptide MftA, and with other genes proposed to convert MftA into the external redox partner mycofactocin.
Ribonucleases (RNases) maintain the cellular RNA pool by RNA processing and degradation. In many bacteria, including the human pathogen Mycobacterium tuberculosis (Mtb), the enzymes mediating several ...central RNA processing functions are still unknown. Here, we identify the hypothetical Mtb protein Rv2179c as a highly divergent exoribonuclease. Although the primary sequence of Rv2179c has no detectable similarity to any known RNase, the Rv2179c crystal structure reveals an RNase fold. Active site residues are equivalent to those in the DEDD family of RNases, and Rv2179c has close structural homology to Escherichia coli RNase T. Consistent with the DEDD fold, Rv2179c has exoribonuclease activity, cleaving the 3' single-strand overhangs of duplex RNA. Functional orthologs of Rv2179c are prevalent in actinobacteria and found in bacteria as phylogenetically distant as proteobacteria. Thus, Rv2179c is the founding member of a new, large RNase family with hundreds of members across the bacterial kingdom.
Rickettsia felis, a Gram‐negative bacterium that causes spotted fever, is of increasing interest as an emerging human pathogen. R. felis and several other Rickettsia strains are classed as National ...Institute of Allergy and Infectious Diseases priority pathogens. In recent years, R. felis has been shown to be adaptable to a wide range of hosts, and many fevers of unknown origin are now being attributed to this infectious agent. Here, the structure of acetoacetyl‐CoA reductase from R. felis is reported at a resolution of 2.0 Å. While R. felis acetoacetyl‐CoA reductase shares less than 50% sequence identity with its closest homologs, it adopts a fold common to other short‐chain dehydrogenase/reductase (SDR) family members, such as the fatty‐acid synthesis II enzyme FabG from the prominent pathogens Staphylococcus aureus and Bacillus anthracis. Continued characterization of the Rickettsia proteome may prove to be an effective means of finding new avenues of treatment through comparative structural studies.
The structure of acetoacetyl‐CoA reductase from Rickettsia felis, the causative agent of flea‐borne spotted fever, is reported. Acetoacetyl‐CoA reductase is a key enzyme in both the glyoxylate/dicarboxylate and butanoate metabolic pathways.
Published biological data suggest that the methyl erythritol phosphate (MEP) pathway, a non-mevalonate isoprenoid biosynthetic pathway, is essential for certain bacteria and other infectious disease ...organisms. One highly conserved enzyme in the MEP pathway is 2C-methyl-d-erythritol 2,4-cyclodiphosphate synthase (IspF). Fragment-bound complexes of IspF from Burkholderia pseudomallei were used to design and synthesize a series of molecules linking the cytidine moiety to different zinc pocket fragment binders. Testing by surface plasmon resonance (SPR) found one molecule in the series to possess binding affinity equal to that of cytidine diphosphate, despite lacking any metal-coordinating phosphate groups. Close inspection of the SPR data suggest different binding stoichiometries between IspF and test compounds. Crystallographic analysis shows important variations between the binding mode of one synthesized compound and the pose of the bound fragment from which it was designed. The binding modes of these molecules add to our structural knowledge base for IspF and suggest future refinements in this compound series.
Entamoeba histolytica is the etiological agent of amebiasis, a diarrheal disease which causes amoebic liver abscesses and amoebic colitis. Approximately 50 million people are infected worldwide with ...E. histolytica. With only 10% of infected people developing symptomatic amebiasis, there are still an estimated 100 000 deaths each year. Because of the emergence of resistant strains of the parasite, it is necessary to find a treatment which would be a proper response to this challenge. ADP‐ribosylation factor (ARF) is a member of the ARF family of GTP‐binding proteins. These proteins are ubiquitous in eukaryotic cells; they generally associate with cell membranes and regulate vesicular traffic and intracellular signalling. The crystal structure of ARF1 from E. histolytica has been determined bound to magnesium and GDP at 1.8 Å resolution. Comparison with other structures of eukaryotic ARF proteins shows a highly conserved structure and supports the interswitch toggle mechanism of communicating the conformational state to partner proteins.
Entamoeba histolytica is the etiological agent of amebiasis, a diarrheal disease which causes amoebic liver abscesses and amoebic colitis. Approximately 50 million people are infected worldwide with ...E. histolytica. With only 10% of infected people developing symptomatic amebiasis, there are still an estimated 100,000 deaths each year. Because of the emergence of resistant strains of the parasite, it is necessary to find a treatment which would be a proper response to this challenge. ADP-ribosylation factor (ARF) is a member of the ARF family of GTP-binding proteins. These proteins are ubiquitous in eukaryotic cells; they generally associate with cell membranes and regulate vesicular traffic and intracellular signalling. The crystal structure of ARF1 from E. histolytica has been determined bound to magnesium and GDP at 1.8 Å resolution. Comparison with other structures of eukaryotic ARF proteins shows a highly conserved structure and supports the interswitch toggle mechanism of communicating the conformational state to partner proteins.
Nucleoside diphosphate kinases (NDKs) are implicated in a wide variety of cellular functions owing to their enzymatic conversion of NDP to NTP. NDK from Borrelia burgdorferi (BbNDK) was selected for ...functional and structural analysis to determine whether its activity is required for infection and to assess its potential for therapeutic inhibition. The Seattle Structural Genomics Center for Infectious Diseases (SSGCID) expressed recombinant BbNDK protein. The protein was crystallized and structures were solved of both the apoenzyme and a liganded form with ADP and vanadate ligands. This provided two structures and allowed the elucidation of changes between the apo and ligand‐bound enzymes. Infectivity studies with ndk transposon mutants demonstrated that NDK function was important for establishing a robust infection in mice, and provided a rationale for therapeutic targeting of BbNDK. The protein structure was compared with other NDK structures found in the Protein Data Bank and was found to have similar primary, secondary, tertiary and quaternary structures, with conserved residues acting as the catalytic pocket, primarily using His132 as the phosphohistidine‐transfer residue. Vanadate and ADP complexes model the transition state of this phosphoryl‐transfer reaction, demonstrating that the pocket closes when bound to ADP, while allowing the addition or removal of a γ‐phosphate. This analysis provides a framework for the design of potential therapeutics targeting BbNDK inhibition.
Structures of Borrelia burgdorferi nucleoside diphosphate kinase have been solved both in the native state and bound to ADP and vanadate to characterize its catalytic action. Visualization strategies and models demonstrate dynamic relationships of the enzyme and ligands, and help to define phosphate transfer by the enzyme. This reaction is important for infection within a mouse model and is a potential target for the development of therapeutics for Lyme disease.
Tyrosyl-DNA phosphodiesterase I (Tdp1) hydrolyzes 3′-phosphotyrosyl bonds to generate 3′-phosphate DNA and tyrosine in vitro. Tdp1 is involved in the repair of DNA lesions created by topoisomerase I, ...although the in vivo substrate is not known. Here we study the kinetic and binding properties of human Tdp1 (hTdp1) to identify appropriate 3′-phosphotyrosyl DNA substrates. Genetic studies argue that Tdp1 is involved in double and single strand break repair pathways; however, x-ray crystal structures suggest that Tdp1 can only bind single strand DNA. Separate kinetic and binding experiments show that hTdp1 has a preference for single-stranded and blunt-ended duplex substrates over nicked and tailed duplex substrate conformations. Based on these results, we present a new model to explain Tdp1/DNA binding properties. These results suggest that Tdp1 only acts upon double strand breaks in vivo, and the roles of Tdp1 in yeast and mammalian cells are discussed.
PDF
