A novel mutation alters the stability of PapA2 resulting in the complete abrogation of sulfolipids in clinical mycobacterial strains

The analysis of whole genomes has revealed specific geographical distribution of Mycobacterium tuberculosis (Mtb) strains across the globe suggestive of unique niche dependent adaptive mechanisms. We provide an important correlation of a genome-based mutation to a molecular phenotype across two predominant clinical Mtb lineages of the Indian subcontinent. We have identified a distinct lineage specific mutation-G247C, translating into an alanine-proline conversion in the papA2 gene of Indo-oceanic lineage 1 (L1) Mtb strains, and restoration of cell wall sulfolipids by simple genetic complementation of papA2 from lineage 3 (L3) or from H37Rv (lineage 4-L4) attributed the loss of this glycolipid to this specific mutation in Indo-Oceanic L1 Mtb. The investigation of structure of Mtb PapA2 revealed a distinct nonribosomal peptide synthetase (NRPS) C domain conformation with an unconventional presence of a zinc binding motif. Surprisingly, the A83P mutation did not map to either the catalytic center in the N-terminal subdomain or any of the substrate-binding region of the protein. On the contrary, the inherent ability of mutant PapA2 to form insoluble aggregates and molecular simulations with the wild-type/mutant (Wt/mut) PapA2 purports an important role for the surface associated 83rd residue in protein conformation. This study demonstrates the importance of a critical structural residue in the papA2 protein of Mtb and helps establish a link between observed genomic alteration and its molecular consequence in the successful human pathogen Mtb. Significance We demonstrate the effect of a unique SNP in PapA2 gene of Indo-oceanic Mycobacterium tuberculosis (Mtb) strains leading to the loss of sulfolipid from these strains. By X-ray crystallographic analysis and molecular dynamics (MD) simulations, we show the importance of this residue in the global PapA2 structure. The presence of a Zn atom has not been reported before for this class of proteins. Here, we provide an important link between genomic alteration and its molecular consequence in Mtb highlighting one of the many adaptive mechanisms that have contributed to its success as a human pathogen. A high degree of identity with PapA1, 3, or 4 would help in interpreting the structure of these PapA proteins and other acyl transferases of other biological systems.

Rv3272 encodes a novel Family III CoA transferase that alters the cell wall lipid profile and protects mycobacteria from acidic and oxidative stress

The availability of complete genome sequence of Mycobacterium tuberculosis has provided an important tool to understand the mycobacterial biology with respect to host-pathogen interaction, which is an unmet need of the hour owing to continuous increasing drug resistance. Hypothetical proteins are often an overlooked pool though half the genome encodes for such proteins of unknown function that could potentially play vital roles in mycobacterial biology. In this context, we report the structural and functional characterization of the hypothetical protein Rv3272. Sequence analysis classifies Rv3272 as a Family III CoA transferase with the classical two domain structure and conserved Aspartate residue (D175). The crystal structure of the wild type protein (2.2 Å) demonstrated the associated inter-locked dimer while that of the D175A mutant co-crystallized with octanoyl-CoA demonstrated relative movement between the two domains. Isothermal titration calorimetry studies indicate that Rv3272 binds to fatty acyl-CoAs of varying carbon chain lengths, with palmitoyl-CoA (C16:0) exhibiting maximum affinity. To determine the functional relevance of Rv3272 in mycobacterial biology, we ectopically expressed Rv3272 in M. smegmatis and assessed that its expression encodes significant alteration in cell surface with marked differences in triacylglycerol accumulation. Additionally, Rv3272 expression protects mycobacteria from acidic, oxidative and antibiotic stress under in vitro conditions. Taken together, these studies indicate a significant role for Rv3272 in host-pathogen interaction.

Role of host- and pathogen-associated lipids in directing the immune response in mycobacterial infections, with emphasis on Mycobacterium avium subsp. paratuberculosis

Mycobacteria have a complex cell wall with a high lipid content that confers unique advantages for bacterial survival in the hostile host environment, leading to long-term infection. There is a wealth of evidence suggesting the role cell wall-associated lipid antigens play at the host-pathogen interface by contributing to bacterial virulence. One pathway that pathogenic mycobacteria use to subvert host immune pathways to their advantage is host cholesterol/lipid homeostasis. This review focuses on the possible role of pathogen- and host-associated lipids in the survival and persistence of pathogenic mycobacteria with emphasis on Mycobacterium avium subsp. paratuberculosis. We draw upon literature in diverse areas of infectious and metabolic diseases and explain a mechanism by which mycobacterial-induced changes in the host cellular energy state could account for phenomena that are a hallmark of chronic mycobacterial diseases.