Three-dimensional models and structure analysis of corynemycolyltransferases in Corynebacterium glutamicum and Corynebacterium efficiens

The Rv3799-Rv3807 Gene Cluster in Mycobacterium Tuberculosis Genome Corresponds to the ‘Ancient Conserved Region’ in CMN Mycolyltransferases

We have identified based on gene cluster analysis that the genes between Rv3799–Rv3807 in M. tuberculosis have orthologs in Corynebacteria, Mycobacteria and Nocardia (CMN) genomes. Therefore, this gene cluster possibly corresponds to the ‘Ancient Conserved Region’ of CMN mycolyltransferases. The evolutionary trace analysis suggests that twelve amino acid residues; Leu39, Trp51, Pro71, Trp82, Trp97, Phe100, Gly124, Ser126, Asp192, Glu230, Gly260 and Trp264 are ‘absolutely conserved’. These amino acid residues constitute the active site and conserved hydrophobic tunnel in CMN mycolyltransferases.

Mycoloyltransferases: A large and major family of enzymes shaping the cell envelope of Corynebacteriales

Mycobacterium and Corynebacterium are important genera of the Corynebacteriales order, the members of which are characterized by an atypical diderm cell envelope. Indeed the cytoplasmic membrane of these bacteria is surrounded by a thick mycolic acid-arabinogalactan-peptidoglycan (mAGP) covalent polymer. The mycolic acid-containing part of this complex associates with other lipids (mainly trehalose monomycolate (TMM) and trehalose dimycolate (TDM)) to form an outer membrane. The metabolism of mycolates in the cell envelope is governed by esterases called mycoloyltransferases that catalyze the transfer of mycoloyl chains from TMM to another TMM molecule or to other acceptors such as the terminal arabinoses of arabinogalactan or specific polypeptides. In this review we present an overview of this family of Corynebacteriales enzymes, starting with their expression, localization, structure and activity to finally discuss their putative functions in the cell. In addition, we show that Corynebacteriales possess multiple mycoloyltransferases encoding genes in their genome. The reason for this multiplicity is not known, as their function in mycolates biogenesis appear to be only partially redundant. It is thus possible that, in some species living in specific environments, some mycoloyltransferases have evolved to gain some new functions. In any case, the few characterized mycoloyltransferases are very important for the bacterial physiology and are also involved in adaptation in the host where they constitute major secreted antigens. Although not discussed in this review, all these functions make them interesting targets for the discovery of new antibiotics and promising vaccines candidates. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.

Serological proteome analysis of Corynebacterium pseudotuberculosis isolated from different hosts reveals novel candidates for prophylactics to control caseous lymphadenitis

Caseous lymphadenitis (CLA) is a highly prevalent disease in goats and sheep worldwide, which is caused by Corynebacterium pseudotuberculosis. Although several prophylactic methods against CLA have been proposed previously, the identification of new C. pseudotuberculosis proteins that are really produced during the infectious process is still needed to improve efficiency and accuracy in vaccines and diagnostics. In this study, we used optimized conditions for serological proteome analysis (SERPA) in order to identify new immune-reactive proteins in C. pseudotuberculosis culture supernatants of two strains, 1002 and C231, isolated from goats and sheep, respectively. Using a sheep and goat serum pool, 13 novel immune-reactive exoproteins common to the two strains were identified. Four of these proteins present known functions and were already described as immune-reactive proteins in other microorganisms, whereas the other nine are of unknown function and show low similarity with proteins from other bacterial species. These data reveal promising targets for immunoprophylactic methods against CLA.

Identification of a mycoloyl transferase selectively involved in O-acylation of polypeptides in Corynebacteriales

We have previously described the posttranslational modification of pore-forming small proteins of Corynebacterium by mycolic acid, a very-long-chain α-alkyl and β-hydroxy fatty acid. Using a combination of chemical analyses and mass spectrometry, we identified the mycoloyl transferase (Myt) that catalyzes the transfer of the fatty acid residue to yield O-acylated polypeptides. Inactivation of corynomycoloyl transferase C (cg0413 [Corynebacterium glutamicum mytC {CgmytC}]), one of the six Cgmyt genes of C. glutamicum, specifically abolished the O-modification of the pore-forming proteins PorA and PorH, which is critical for their biological activity. Expectedly, complementation of the cg0413 mutant with either the wild-type gene or its orthologues from Corynebacterium diphtheriae and Rhodococcus, but not Nocardia, fully restored the O-acylation of the porins. Consistently, the three-dimensional structure of CgMytC showed the presence of a unique loop that is absent from enzymes that transfer mycoloyl residues onto both trehalose and the cell wall arabinogalactan. These data suggest the implication of this structure in the enzyme specificity for protein instead of carbohydrate.

Docking of phosphonate and trehalose analog inhibitors into M. tuberculosis mycolyltransferase Ag85C: Comparison of the two scoring fitness functions GoldScore and ChemScore, in the GOLD software

The Ag85 family enzymes are responsible for the synthesis of cell wall components in mycobacterial species. Inhibitors to these enzymes are potential antimycobacterial agents. We have carried out the docking of phoshonate and trehalose analog inhibitors into the three dimensional structure of mycolyltransferase enzyme, Ag85C of M. tuberculosis using the GOLD software. The inhibitor binding positions and affinity were evaluated using both the scoring fitness functions- GoldScore and ChemScore. We observed that the inhibitor binding position identified using the GoldScore was marginally better than the ChemScore. A qualitative agreement between the reported experimental biological activities (IC50) and the GoldScore was observed. We identified that amino acid residues Arg541, Trp762 are important for inhibitor recognition via hydrogen bonding interactions. This information can be exploited to design Ag85C specific inhibitors.

Analysis and modeling of mycolyl-transferases in the CMN group

Mycolyl-transferases are a family of proteins that are specifically present in the CMN (Corynebacterium, Mycobacterium and Nocardia) genera and are responsible for the synthesis of cell wall components. We modeled the three-dimensional structures of mycolyl-transfersases from Corynebacterium and Nocardia using homology modeling methods based on the crystal structures of mycolyl-transferases from M. tuberculosis. Comparison of the models revealed significant differences in their substrate binding site. Some mycolyl-transferases identified by the following Gene Ids: Nfa25110, Nfa45560, Nfa7210, Nfa38260, Nfa32420, Nfa23770, Nfa43800, Nfa30260, Dip0365, Ncgl0987, Ce1488, Ncgl0885, Ce0984, Ncgl2101, Ncgl0336, Ce0356 are associated with a relatively larger substrate binding site and amino acid residue mutations (D40N, R43D/G, S236N/A) are likely to affect binding to trehalose.