Bacterial species exhibit diversity in their mechanisms and capacity for protein disulfide bond formation

Abstract

Protein disulfide bond formation contributes to the folding and activity of many exported proteins in bacteria. However, information about disulfide bond formation is limited to only a few bacterial species. We used a multifaceted bioinformatic approach to assess the capacity for disulfide bond formation across this biologically diverse group of organisms. We combined data from a cysteine counting method, in which a significant bias for even numbers of cysteine in proteins is taken as an indicator of disulfide bond formation, with data on the presence of homologs of known disulfide bond formation enzymes. These combined data enabled us to make predictions about disulfide bond formation in the cell envelope across bacterial species. Our bioinformatic and experimental results suggest that many bacteria may not generally oxidatively fold proteins, and implicate the bacterial homolog of the enzyme vitamin K epoxide reductase, a protein required for blood clotting in humans, as part of a disulfide bond formation pathway present in several major bacterial phyla.cysteine ͉ genomics ͉ protein folding ͉ vitamin K epoxide reductase

The Corynebacterium diphtheriae shaft pilin SpaA is built of tandem Ig-like modules with stabilizing isopeptide and disulfide bonds

“…SpaA additionally contains a disulfide bond, conserved in the other C. diphtheriae major pilins, which might be expected to further enhance stability. The major pilins of S. pyogenes, B. cereus, and S. pneumoniae lack Cys residues, however, and given that many Gram-positive bacteria lack the disulfide formation machinery of Gram-negative bacteria (25,26), we speculate that isopeptide bonds have evolved as an alternative means of stabilization. As amide bonds they would also be less prone to chemical disruption than disulfide bonds, a property that may be important for such thin, exposed assemblies, which do not seem to form higher-order bundles.…”

Vitamin K epoxide reductase prefers ER membrane-anchored thioredoxin-like redox partners

“…This fifth TM segment does not directly contribute to the enzymatic mechanism, but interacts with the core of VKOR and positions the Trx-like domain for catalysis. Several other bacterial and plant species also have VKORs that are fused through an additional TM segment with a periplasmic/ER-luminal Trx-like domain (6)(7)(8). However, there are many species in which VKORs must cooperate with a separately encoded redox partner.…”

“…Homologs of VKOR have been identified in many organisms, even species that do not have blood (6)(7)(8). These include several classes of bacteria in which these enzymes are involved in disulfide bridge formation of newly synthesized secretory proteins (7)(8)(9)(10).…”

“…These include several classes of bacteria in which these enzymes are involved in disulfide bridge formation of newly synthesized secretory proteins (7)(8)(9)(10). The reduced cysteines of exported proteins are initially oxidized by a Trx-like protein in the periplasm, leading to the reduction of the disulfide bridge in the active site CXXC motif of the Trx-like protein.…”

Insight Into Genes Involved in the Production of Extracellular Chitinase in a Biocontrol Bacterium Lysobacter enzymogenes C-3

“…The Dsb components in the periplasm of bacteria have been proposed to play important role in the secretion of virulence factors, such as adhesion, toxin production, secretion of extracellular enzymes and motility, in various bacteria (Dutton et al, 2008;Heras et al, 2009). We hypothesized that the extracellular chitinase enzyme(s) might be secreted through the Dsb pathway in the periplasm, and that the Dsb components are required for active extracellular chitinase formation in L. enzymogenes C-3 as described for E. coli (Dutton et al, 2008: Heras et al, 2009. To test our hypothesis, we are currently constructing Dsb mutants.…”