6n42

Publication Abstract from PubMed

Cysteine dioxygenase (CDO) is a non-heme iron enzyme that adds two oxygen atoms from dioxygen to the sulfur atom of L-cysteine. Adjacent to the iron site of mammalian CDO, a post-translationally generated Cys-Tyr cofactor is present, whose presence substantially enhances the oxygenase activity. The formation of the Cys-Tyr cofactor in CDO is an autocatalytic process, and it is challenging to study by traditional techniques because the crosslinking reaction is a side, uncoupled, single-turnover oxidation buried among multiple turnovers of L-cysteine oxygenation. Here, we take advantage of our recent success in obtaining a purely uncrosslinked human CDO due to site-specific incorporation 3,5-difluoro-L-tyrosine (F2-Tyr) at the crosslinking site through the genetic code expansion strategy. Using EPR spectroscopy, we show that nitric oxide (*NO), an oxygen surrogate, similarly binds to uncrosslinked F2-Tyr157 CDO as in wild-type human CDO. We determined X-ray crystal structures of uncrosslinked F2-Tyr157 CDO and mature wild-type CDO in complex with both L-cysteine and *NO. These structural data reveal that the active site cysteine (Cys93 in the human enzyme), rather than the generally expected tyrosine (i.e., Tyr157), is well aligned to be oxidized should the normal oxidation reaction uncouple. This structural-based understanding is further supported by a computational study with models built on the uncrosslinked ternary complex structure. Together, these results strongly suggest that the first target to oxidize during the iron-assisted Cys-Tyr cofactor biogenesis is Cys93. Based on these data, a plausible reaction mechanism implementing a cysteine radical involved in the crosslink formation is proposed.

Probing the Tyr-Cys Cofactor Biogenesis in Cysteine Dioxygenase by the Genetic Incorporation of Fluorotyrosine.,Li J, Koto T, Davis I, Liu A Biochemistry. 2019 Apr 4. doi: 10.1021/acs.biochem.9b00006. PMID:30946568^[1]

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