Probing the Substrate Specificity and Protein-Protein Interactions of the E. coli Fatty Acid Dehydratase, FabA

Microbial fatty acid biosynthetic enzymes are important targets for areas as diverse as antibiotic development to biofuel production. Elucidating the molecular basis of chain length control during fatty acid biosynthesis is crucial for the understanding of regulatory processes of this fundamental metabolic pathway. In Escherichia coli, the acyl carrier protein (AcpP) plays a central role by sequestering and shuttling the growing acyl chain between fatty acid biosynthetic enzymes. FabA, a β-hydroxyacyl-AcpP dehydratase, is an important enzyme in controlling fatty acid chain length and saturation levels. FabA-AcpP interactions are transient in nature and thus difficult to visualize. In this study, four mechanistic crosslinking probes mimicking varying acyl chain lengths were synthesized to systematically probe for modified chain length specificity of 14 FabA mutants. These studies provide evidence for the AcpP-interacting "positive patch," FabA mutations that alter substrate specificity, and the roles that the FabA "gating residues" play in chain length control.