title: A radical intermediate in tyrosine scission to the CO and CN- ligands of FeFe hydrogenase.
abstract: The radical S-adenosylmethionine (SAM) enzyme HydG lyses free l-tyrosine to produce CO and CN(-) for the assembly of the catalytic H cluster of FeFe hydrogenase. We used electron paramagnetic resonance spectroscopy to detect and characterize HydG reaction intermediates generated with a set of (2)H, (13)C, and (15)N nuclear spin-labeled tyrosine substrates. We propose a detailed reaction mechanism in which the radical SAM reaction, initiated at an N-terminal 4Fe-4S cluster, generates a tyrosine radical bound to a C-terminal 4Fe-4S cluster. Heterolytic cleavage of this tyrosine radical at the Cα-Cβ bond forms a transient 4-oxidobenzyl (4OB(•)) radical and a dehydroglycine bound to the C-terminal 4Fe-4S cluster. Electron and proton transfer to this 4OB(•) radical forms p-cresol, with the conversion of this dehydroglycine ligand to Fe-bound CO and CN(-), a key intermediate in the assembly of the 2Fe subunit of the H cluster.
authors.affiliation: Department of Chemistry, University of California, Davis, Davis, CA 95616, USA.
authors.forename: Jon M
authors.initials: JM
authors.lastname: Kuchenreuther
authors.forename: William K
authors.initials: WK
authors.lastname: Myers
authors.forename: Troy A
authors.initials: TA
authors.lastname: Stich
authors.forename: Simon J
authors.initials: SJ
authors.lastname: George
authors.forename: Yaser
authors.initials: Y
authors.lastname: Nejatyjahromy
authors.forename: James R
authors.initials: JR
authors.lastname: Swartz
authors.forename: R David
authors.initials: RD
authors.lastname: Britt
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D002248:Carbon Monoxide / Q000737:chemistry; D002384:Catalysis; D020134:Catalytic Domain; D006864:Hydrogenase / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000235:genetics; D008024:Ligands; D012436:S-Adenosylmethionine / Q000737:chemistry; D020592:Shewanella / Q000201:enzymology*; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D007506:Iron-Sulfur Proteins; D008024:Ligands; D014443:Tyrosine; D012436:S-Adenosylmethionine; D002248:Carbon Monoxide; C118830:iron hydrogenase; D006864:Hydrogenase