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

Abstract

The analysis of whole genome has revealed specific geographical distribution of Mycobacterium tuberculosis (Mtb) strains across the globe suggestive of unique host dependent adaptive mechanisms in Mtb evolved out of selective pressures. 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 to proline conversion in the papA2 gene of Indo oceanic lineage 1 [L1] Mtb strains; 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. Investigation into the structure of Mtb PapA2 revealed a distinct non-ribosomal peptide synthetase (NRPS) C domain conformation with an unconventional presence of Zinc binding motif. Surprisingly, the A83P mutation did not map to either the catalytic centre 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 Wt/ mut PapA2 purports an important role for the surface associated 83rd residue in protein conformation. The present 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.