Structural investigation of the docking domain assembly from trans-AT polyketide synthases

Docking domains (DDs) located at the C- and N-termini of polypeptides play a crucial role in directing the assembly of polyketide synthases (PKSs), which are multienzyme complexes. Here, we determined the crystal structure of a complex comprising the C-terminal DD (^CDD_MlnB) and N-terminal DD (^NDD_MlnC) of macrolactin trans-acyltransferase (AT) PKS that were fused to a functional enzyme, AmpC EC2 β-lactamase. Interface analyses of the ^CDD_MlnB/^NDD_MlnC complex revealed the molecular intricacies in the core section underpinning the precise DD assembly. Additionally, circular dichroism and steady-state kinetics demonstrated that the formation of the ^CDD_MlnB/^NDD_MlnC complex had no influence on the structural and functional fidelity of the fusion partner, AmpC EC2. This inspired us to apply the ^CDD_MlnB/^NDD_MlnC assembly to metabolon engineering. Indeed, DD assembly induced the formation of a complex between 4-coumarate-CoA ligase and chalcone synthase both involved in flavonoid biosynthesis, leading to a remarkable increase in naringenin production in vitro.