Transacylation Kinetics in Fatty Acid and Polyketide Synthases and its Sensitivity to Point Mutations**

Fatty acid and polyketide synthases (FASs and PKSs) synthesize physiologically and pharmaceutically important products by condensation of acyl building blocks. The transacylation reaction catalyzed by acyl transferases (ATs) is responsible for the selection of acyl-CoA esters for further processing by FASs and PKSs. In this study, the AT domains of different multidomain (type I) PKS systems are kinetically described in their substrate selectivity, AT-Acyl carrier protein (ACP) domain-domain interaction and enzymatic kinetic properties. We observe that the ATs of modular PKSs, intricate protein complexes occurring in bacteria and responsible for the biosynthesis of bioactive polyketides, are significantly slower than ATs of mammalian FASs, reflecting the respective purpose of the biosynthetic pathways within the organism and their metabolic context. We further perform a mutational study on the kinetics of the AT-ACP interaction in the modular PKS 6-deoxyerythronolide B synthase (DEBS) and find a high plasticity in enzyme properties, which we explain by a high plasticity in AT-ACP recognition. Our study enlarges the understanding of ATs in its molecular properties and is similarly a call for thorough AT-centered PKS engineering strategies.

Automated summary

This study investigates the mechanisms of FASs and PKSs in synthesizing important products and the substrate selectivity and enzymatic properties of different ATs. Findings reveal that ATs in PKS systems occurring in bacteria are slower than ATs in mammalian FASs, reflecting the respective purposes and metabolic contexts within the organism.