YASH and GHSXG motifs of ZmaA-AT compared to a methylmalonyl-CoA specific AT.

The substrate binding-pocket amino acid residues (290–300 and 194) of ZmaA-AT (blue, with white span for disordered 293–295) are superimposed on those of AT from the DEB PKS module 3 (wheat). Bulky F193 is found next to the active site S192 in ZmaA-AT, instead of the glutamine residue found in methylmalonyl-CoA specific ATs. The catalytic H297 is positioned similarly to other ATs, despite its proposed steric hindrance to extender units with (2R) conformations. Despite high mobility for the substrate pocket lid YASH motif, we conclude based on the positions of well-ordered flanking residues that they must wander within the substrate binding pocket of ZmaA-AT, which holds co-crystallized formate (spheres). The red box, with its marked corner, can be compared to the same box in Figure 2 in order to orient the reader.