4 '-phosphopantetheine transfer in primary and secondary metabolism of Bacillus subtilis

4'-Phosphopantetheine transferases (PPTases) transfer the 4'-phosphopanteth eine moiety of coenzyme A onto a conserved serine residue of acyl carrier p roteins (ACPs) of fatty acid and polyketide synthases as well as peptidyl c arrier proteins (PCPs) of nonribosomal peptide synthetases. This posttransl ational modification converts ACPs and PCPs from their inactive apo into th e active holo form. We have investigated the 4'-phosphopantetheinylation re action in Bacillus subtilis, an organism containing in total 43 ACPs and PC Ps but only two PPTases, the acyl carrier protein synthase AcpS of primary metabolism and Sfp, a PPTase of secondary metabolism associated with the no nribosomal peptide synthetase for the peptide antibiotic surfactin. We iden tified and cloned ydcB encoding AcpS from B. subtilis, which complemented a n Escherichia coli acps disruption mutant. B. subtilis AcpS and its substra te ACP were bio chemically characterized. AcpS also modified the D-alanyl c arrier protein but failed to recognize PCP and an acyl carrier protein of s econdary metabolism discovered in this study, designated AcpK, that was not identified by the Bacillus genome project. On the other hand, Sfp was able to modify in vitro all acyl carrier proteins tested. We thereby extend the reported broad specificity of this enzyme to the homologous ACP. This in v itro cross-interaction between primary and secondary metabolism was confirm ed under physiological in vivo conditions by the construction of a ydcB del etion in a B. subtilis sfp(+) strain. The genes coding for Sfp and its homo log Gsp from Bacillus brevis could also complement the E. coli acps disrupt ion. These results call into question the essential role of AcpS in strains that contain a Sfp-like PPTase and consequently the suitability of AcpS as a microbial target in such strains.