One residue substitution in PcyA leads to unexpected changes in tetrapyrrole substrate binding

► PcyA catalyzes the reduction of the biliverdin IXα. ► Structure of PcyA V225D protein revealed the gross changes of the substrate-binding pocket. ► Induced-fit did not occur unlike wild-type PcyA upon substrate binding to the V225D protein. ► Binding manner of the substrate in V225D was entirely different from that in wild-type PcyA.