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Caltech

Inorganic-Electrochemistry Seminar

Friday, January 17, 2014
4:00pm to 5:00pm
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Noyes 147 (J. Holmes Sturdivant Lecture Hall)
Assembling the H-Cluster of [FeFe] Hydrogenase
R. David Britt, Professor and Chairman, Department of Chemistry, Chemistry, University of California, Davis,

 

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 use electron paramagnetic resonance (EPR) spectroscopy to detect and characterize HydG reaction intermediates generated with a set of  2H, 13C, and 15N 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  Calpha-Cbeta 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 (1). We apply stopped-flow Fourier transform infrared (SF-FTIR) and electron-nuclear double resonance (ENDOR) spectroscopies to explore in detail the formation of HydG-bound Fe-containing species bearing  CO and CN- ligands, with spectroscopic signatures that evolve on the 1 to 1000 s timescale. Through study of the 13C, 15N, and 57Fe isotopologues of these intermediates and products, we identify   the final HydG-bound species as an organometallic Fe(CO)2CN synthon that is ultimately transferred to apo-hydrogenase to form the  [2Fe]H component of the H-cluster (2).

 

References 

1. Jon M. Kuchenreuther, William K. Myers, Troy A. Stich, Simon J. George , Yaser NejatyJahromy, James R. Swartz, and  R. David Britt. "A Radical Intermediate in  Tyrosine Scission to the CO and CN- Ligands of [FeFe] Hydrogenase"  Science (2013) 342:472-475

2. Jon M. Kuchenreuther, William K. Myers, Daniel L. M. Suess, Troy A. Stich, Vladimir Pelmenschikov, Stacey A. Shiigi, Stephen P. Cramer, James R. Swartz, R. David Britt, and Simon J. George "The  HydG  Enzyme Generates an Fe(CO)2(CN) Synthon in the Biosynthesis of the FeFe Hydrogenase H-Cluster"  Science (2013) in press.

 
For more information, please contact Patricia Anderson by phone at 626-395-6022 or by email at [email protected].