Crystal structure of I86D mutated PcyA in complex with biliverdin

What is it about?

Phycocyanobilin:ferredoxin oxidoreductase (PcyA) catalyzes the reduction of biliverdin (BV) to produce phycocyanobilin, a linear tetrapyrrole pigment for light-harvesting and light-sensing. Spectroscopic and HPLC analyses imply that BV bound to I86D mutant of PcyA is fully protonated (BVH+) and can accept an electron, but I86D is unable to donate protons for the reduction. To elucidate the structural basis of I86D, we determined the atomic resolution structure of the I86D–BVH+ complex, and the protonation states of the essential residues, Asp105 and Glu76. Asp105 adopted one conformation in I86D, although that had dual conformation in the wild-type PcyA, reflecting the protonation state of BV. Together with biochemical/spectroscopic results, the I86D–BVH+ structure supports that the flexibility of Asp105 is essential for the PcyA reaction.

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