Download MendeleyStructure-Based Mechanism for Oxidative Decarboxylation Reactions Mediated by Amino Acids and Heme Propionates in Coproheme Decarboxylase (HemQ).
Celis, A.I., Gauss, G.H., Streit, B.R., Shisler, K., Moraski, G.C., Rodgers, K.R., Lukat-Rodgers, G.S., Peters, J.W., DuBois, J.L.(2017) J Am Chem Soc 139: 1900-1911
- PubMed: 27936663
- DOI: https://doi.org/10.1021/jacs.6b11324
- Primary Citation of Related Structures:
5T2K - PubMed Abstract:
Coproheme decarboxylase catalyzes two sequential oxidative decarboxylations with H 2 O 2 as the oxidant, coproheme III as substrate and cofactor, and heme b as the product. Each reaction breaks a C-C bond and results in net loss of hydride, via steps that are not clear. Solution and solid-state structural characterization of the protein in complex with a substrate analog revealed a highly unconventional H 2 O 2 -activating distal environment with the reactive propionic acids (2 and 4) on the opposite side of the porphyrin plane. This suggested that, in contrast to direct C-H bond cleavage catalyzed by a high-valent iron intermediate, the coproheme oxidations must occur through mediating amino acid residues. A tyrosine that hydrogen bonds to propionate 2 in a position analogous to the substrate in ascorbate peroxidase is essential for both decarboxylations, while a lysine that salt bridges to propionate 4 is required solely for the second. A mechanism is proposed in which propionate 2 relays an oxidizing equivalent from a coproheme compound I intermediate to the reactive deprotonated tyrosine, forming Tyr • . This residue then abstracts a net hydrogen atom (H • ) from propionate 2, followed by migration of the unpaired propionyl electron to the coproheme iron to yield the ferric harderoheme and CO 2 products. A similar pathway is proposed for decarboxylation of propionate 4, but with a lysine residue as an essential proton shuttle. The proposed reaction suggests an extended relay of heme-mediated e - /H + transfers and a novel route for the conversion of carboxylic acids to alkenes.
Organizational Affiliation:
Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717-3400, United States.
