A conserved motif flags acyl carrier proteins for β-branching in polyketide synthesis
Haines, Anthony S Song, Zhongshu Farmer, Rohit Williams, Christopher Hothersall, Joanne Płoskoń, Eliza Wattana-Amorn, Pakorn Stephens, Elton R Yamada, Erika Gurney, Rachel Takebayashi, Yuiko Masschelein, Joleen Cox, Russell J Lavigne, Rob Willis, Christine L Simpson, Thomas J Crosby, John Winn, Peter J Thomas, Christopher M Crump, Matthew P # ×
Nature Pub. Group
Nature chemical biology vol:9 issue:11 pages:685-92
Type I polyketide synthases often use programmed β-branching, via enzymes of a 'hydroxymethylglutaryl-CoA synthase (HCS) cassette', to incorporate various side chains at the second carbon from the terminal carboxylic acid of growing polyketide backbones. We identified a strong sequence motif in acyl carrier proteins (ACPs) where β-branching is known to occur. Substituting ACPs confirmed a correlation of ACP type with β-branching specificity. Although these ACPs often occur in tandem, NMR analysis of tandem β-branching ACPs indicated no ACP-ACP synergistic effects and revealed that the conserved sequence motif forms an internal core rather than an exposed patch. Modeling and mutagenesis identified ACP helix III as a probable anchor point of the ACP-HCS complex whose position is determined by the core. Mutating the core affects ACP functionality, whereas ACP-HCS interface substitutions modulate system specificity. Our method for predicting β-carbon branching expands the potential for engineering new polyketides and lays a basis for determining specificity rules.