Neglected tropical diseases in Australia: a narrative review

Multi-epitope vaccine candidates based on mycobacterial membrane protein large (MmpL) proteins against Mycobacterium ulcerans

Buruli ulcer (BU) is a neglected tropical disease. It is caused by the bacterium Mycobacterium ulcerans and is characterized by skin lesions. Several studies were performed testing the Bacillus Calmette-Guérin (BCG) vaccine in human and animal models and M. ulcerans-specific vaccines in animal models. However, there are currently no clinically accepted vaccines to prevent M. ulcerans infection. The aim of this study was to identify T-cell and B-cell epitopes from the mycobacterial membrane protein large (MmpL) proteins of M. ulcerans. These epitopes were analysed for properties including antigenicity, immunogenicity, non-allergenicity, non-toxicity, population coverage and the potential to induce cytokines. The final 8 CD8+, 12 CD4+ T-cell and 5 B-cell epitopes were antigenic, non-allergenic and non-toxic. The estimated global population coverage of the CD8+ and CD4+ epitopes was 97.71%. These epitopes were used to construct five multi-epitope vaccine constructs with different adjuvants and linker combinations. The constructs underwent further structural analyses and refinement. The constructs were then docked with Toll-like receptors. Three of the successfully docked complexes were structurally analysed. Two of the docked complexes successfully underwent molecular dynamics simulations (MDS) and post-MDS analysis. The complexes generated were found to be stable. However, experimental validation of the complexes is required.

The oxidation of cholesterol derivatives by the CYP124 and CYP142 enzymes from Mycobacterium marinum

The CYP124 and CYP142 families of bacterial cytochrome P450 monooxygenases (CYPs), catalyze the oxidation of methyl branched lipids, including cholesterol, as one of the initial activating steps in their catabolism. Both enzymes are reported to supplement the CYP125 family of P450 enzymes. These CYP125 enzymes are found in the same bacteria, and are the primary cholesterol/cholest-4-en-3-one metabolizing enzymes. To further understand the role of the CYP124 and CYP142 cytochrome P450s we investigated the Mycobacterium marinum enzymes, MmarCYP124A1 and CYP142A3, with various cholesterol analogues with modifications on the A and B rings of the steroid. We assessed the substrate binding and catalytic activity of each enzyme. Neither enzyme could bind or oxidize cholesteryl acetate or 3,5-cholestadiene, which have modifications at the C3 hydroxyl moiety of cholesterol. The CYP142 enzyme was better able to accommodate and oxidize cholesterol analogues which have changes on the A/B rings including cholesterol-5α,6α-epoxide and diastereomers of 5-cholestan-3-ol. The CYP124 enzyme was more tolerant of changes at C7 of the cholesterol B ring, e.g., 7-ketocholesterol than in the A ring. The selectivity for oxidation at the ω-carbon of a branched chain was observed in all steroids that were oxidized. The 7-ketocholesterol-bound MmarCYP124A1 enzyme from M. marinum, was structurally characterized by X-ray crystallography to 1.81Å resolution. The 7-ketocholesterol-bound X-ray crystal structure of the MmarCYP124A1 enzyme revealed that the substrate binding mode of this cholesterol derivative was altered compared to those observed with other non-steroidal ligands. The structure provided an explanation for the selectivity of the enzyme for terminal methyl hydroxylation.