Binding modes of βK and putative catalytic mechanisms of βK-incorporation. A) βK is placed in the primary funnel (blue tube) as in the MD simulation E1: no space is left to host the thioester carrier CoA/ACP. B) The access of ACoA into the primary funnel is hindered with βK in the pose as in A. C) βK is in the secondary channel (violet box) as in the MD simulations E2a and E2b: in the primary funnel space is available to accommodate the thioester carrier CoA/ACP. D) ACoA can access the primary funnel with βK in this pose and transfer anthranilate to Cys112. E) The Claisen condensation fits best as mechanism for βK incorporation for βK in the primary funnel. F) The imine/enamine formation is the most plausible mechanism for βK incorporation when βK is in the secondary channel.