抗酸菌症
オープンアクセス

概要

Functional and structural flexibility of Type III polyketide synthases in mycobacterium marinum

Priti Saxena1*, Samir Giri1, Amreesh Parvez1, Gorkha Raj Giri1, Shivendra Pratap2, Monika Kumari1, Abhiruchi Kant2, Renu Bisht1 and Vengadesan Krishnan2

Mycobacterial pathogenesis is hallmarked by lipidic polyketides that decorate cell envelope and mediate infection. However, factors mediating persistence remain largely unknown. Dynamic cell wall remodeling could facilitate different pathogenic phases. Recent studies have implicated type III polyketide synthases (PKSs) in cell wall alterations in several bacteria. Comparative genome analysis revealed several type III pks genes in mycobacteria. Mycobacterium marinum genome harbors four type III pkss that group into three pks genomic clusters. mmar_2470 and mmar_2474 form a cluster with other type I pkss, while mmar_2190 is grouped with genes for several polyketide modifiers. Interestingly, these unique pks genomic clusters are conserved exclusively in pathogenic species. Cell-free reconstitution assays and high-resolution mass spectrometric analyses revealed capability of these proteins to accept various monocarboxyl-CoA substrates and extend with dicarboxyl-CoA extender units to biosynthesize a palette of polyketide metabolites. MMAR_2470 and MMAR_2474 proteins utilized two different extenders to biosynthesize methylated polyketide products while MMAR_2190 produced non-methylated metabolites. Three-dimensional structural analyses for MMAR_2190 revealed a distinct catalytic functioning regulated by rotational flexibility of key active site amino acids. Functional investigations in heterologous mycobacterial strain implicated these proteins to be vital for mycobacterial survival in stationary biofilms. Our study provides new insights on functional importance of type III PKSs conserved in pathogenic mycobacterial species and delineates mechanistically crucial residue positions that can be modulated to generate a repertoire of unusual biologically active type III polyketides.