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Publication Abstract from PubMed

Thiol dioxygenases are a subset of non-heme iron oxygenases that catalyze the formation of sulfinic acids from sulfhydryl-containing substrates and dioxygen. Among this class, cysteine dioxygenases (CDOs) and 3-mercaptopropionic acid dioxygenases (3MDOs) are the best characterized, and the mode of substrate binding for CDOs is well understood. However, the manner in which 3-mercaptopropionic acid (3MPA) coordinates to the non-heme iron site in 3MDO remains matters of debate. A model for bidentate 3MPA-coordination at the 3MDO Fe-site has been proposed on the basis of computational docking, whereas steady-state kinetics and EPR spectroscopic measurements suggest a thiolate-only coordination of the substrate. To address this gap in knowledge, we determined the structure of Azobacter vinelandii 3MDO (Av3MDO) in complex with the substrate analog and competitive inhibitor, 3-hydroxypropionic acid (3HPA). The structure together with DFT computational modeling demonstrate that 3HPA (and 3MPA) associate with iron as chelate complexes with the substrate-carboxylate group forming an additional interaction with Arg168 and the thiol bound at the same position as in CDO. A chloride ligand was bound to iron in the coordination site assigned as the O2-binding site. Supporting HYSCORE spectroscopic experiments were performed on the (3MPA/NO)-bound Av3MDO iron nitrosyl (S = 3/2) site. In combination with spectroscopic simulations and optimized DFT models, this work provides an experimentally verified model of the Av3MDO enzyme-substrate complex, effectively resolving a debate in the literature regarding the preferred substrate-binding denticity. These results elegantly explain the observed 3MDO substrate-specificity, but leave unanswered questions regarding the mechanism of substrate-gated reactivity with dioxygen.

Structure of 3-mercaptopropionic acid dioxygenase with a substrate analog reveals bidentate substrate binding at the iron center.,York NJ, Lockart MM, Sardar S, Khadka N, Shi W, Stenkamp RE, Zhang J, Kiser PD, Pierce BS J Biol Chem. 2021 Mar 1:100492. doi: 10.1016/j.jbc.2021.100492. PMID:33662397^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.