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Title: Extended X-Ray Absorption Fine Structure And Nuclear Resonance Vibrational Spectroscopy Reveal That NifB-Co, a FeMo-Co Precursor, Comprises a 6Fe Core With An Interstitial Light Atom

Abstract

NifB-co, an Fe-S cluster produced by the enzyme NifB, is an intermediate on the biosynthetic pathway to the iron molybdenum cofactor (FeMo-co) of nitrogenase. We have used Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy together with {sup 57}Fe nuclear resonance vibrational spectroscopy (NRVS) to probe the structure of NifB-co while bound to the NifX protein from Azotobacter vinelandii. The spectra have been interpreted in part by comparison with data for the completed FeMo-co attached to the NafY carrier protein: the NafY:FeMo-co complex. EXAFS analysis of the NifX:NifB-co complex yields an average Fe-S distance of 2.26 {angstrom} and average Fe-Fe distances of 2.66 and 3.74 {angstrom}. Search profile analyses reveal the presence of a single Fe-X (X = C, N, or O) interaction at 2.04 {angstrom}, compared to a 2.00 {angstrom} Fe-X interaction found in the NafY:FeMo-co EXAFS. This suggests that the interstitial light atom (X) proposed to be present in FeMo-co has already inserted at the NifB-co stage of biosynthesis. The NRVS exhibits strong bands from Fe-S stretching modes peaking around 270, 315, 385, and 408 cm{sup -1}. Additional intensity at {approx} 185-200 cm{sup -1} is interpreted as a set of cluster 'breathing' modes similar to those seenmore » for the FeMo-cofactor. The strength and location of these modes also suggest that the FeMo-co interstitial light atom seen in the crystal structure is already in place in NifB-co. Both the EXAFS and NRVS data for NifX:NifB-co are best simulated using a Fe{sub 6}S{sub 9}X trigonal prism structure analogous to the 6Fe core of FeMo-co, although a 7Fe structure made by capping one trigonal 3S terminus with Fe cannot be ruled out. The results are consistent with the conclusion that the interstitial light atom is already present at an early stage in FeMo-co biosynthesis prior to the incorporation of Mo and R-homocitrate.« less

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
953160
Report Number(s):
SLAC-REPRINT-2009-124
TRN: US200914%%355
DOE Contract Number:  
AC02-76SF00515
Resource Type:
Journal Article
Journal Name:
J. Am. Chem. Soc. 130:5673,2008
Additional Journal Information:
Journal Volume: 130; Journal Issue: 17
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION; ATOMS; AZOTOBACTER; BIOSYNTHESIS; CRYSTAL STRUCTURE; ENZYMES; FINE STRUCTURE; INTERSTITIALS; IRON; MOLYBDENUM; NITROGENASE; PRECURSOR; PRISMS; PROBES; PROTEINS; RESONANCE; RESPIRATION; SPECTRA; SPECTROSCOPY; Other,CHEM

Citation Formats

George, S J, Igarashi, R Y, Xiao, Y, Hernandez, J A, Demuez, M, Zhao, D, Yoda, Y, Ludden, P W, Rubio, L M, and Cramer, S P. Extended X-Ray Absorption Fine Structure And Nuclear Resonance Vibrational Spectroscopy Reveal That NifB-Co, a FeMo-Co Precursor, Comprises a 6Fe Core With An Interstitial Light Atom. United States: N. p., 2009. Web.
George, S J, Igarashi, R Y, Xiao, Y, Hernandez, J A, Demuez, M, Zhao, D, Yoda, Y, Ludden, P W, Rubio, L M, & Cramer, S P. Extended X-Ray Absorption Fine Structure And Nuclear Resonance Vibrational Spectroscopy Reveal That NifB-Co, a FeMo-Co Precursor, Comprises a 6Fe Core With An Interstitial Light Atom. United States.
George, S J, Igarashi, R Y, Xiao, Y, Hernandez, J A, Demuez, M, Zhao, D, Yoda, Y, Ludden, P W, Rubio, L M, and Cramer, S P. 2009. "Extended X-Ray Absorption Fine Structure And Nuclear Resonance Vibrational Spectroscopy Reveal That NifB-Co, a FeMo-Co Precursor, Comprises a 6Fe Core With An Interstitial Light Atom". United States.
@article{osti_953160,
title = {Extended X-Ray Absorption Fine Structure And Nuclear Resonance Vibrational Spectroscopy Reveal That NifB-Co, a FeMo-Co Precursor, Comprises a 6Fe Core With An Interstitial Light Atom},
author = {George, S J and Igarashi, R Y and Xiao, Y and Hernandez, J A and Demuez, M and Zhao, D and Yoda, Y and Ludden, P W and Rubio, L M and Cramer, S P},
abstractNote = {NifB-co, an Fe-S cluster produced by the enzyme NifB, is an intermediate on the biosynthetic pathway to the iron molybdenum cofactor (FeMo-co) of nitrogenase. We have used Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy together with {sup 57}Fe nuclear resonance vibrational spectroscopy (NRVS) to probe the structure of NifB-co while bound to the NifX protein from Azotobacter vinelandii. The spectra have been interpreted in part by comparison with data for the completed FeMo-co attached to the NafY carrier protein: the NafY:FeMo-co complex. EXAFS analysis of the NifX:NifB-co complex yields an average Fe-S distance of 2.26 {angstrom} and average Fe-Fe distances of 2.66 and 3.74 {angstrom}. Search profile analyses reveal the presence of a single Fe-X (X = C, N, or O) interaction at 2.04 {angstrom}, compared to a 2.00 {angstrom} Fe-X interaction found in the NafY:FeMo-co EXAFS. This suggests that the interstitial light atom (X) proposed to be present in FeMo-co has already inserted at the NifB-co stage of biosynthesis. The NRVS exhibits strong bands from Fe-S stretching modes peaking around 270, 315, 385, and 408 cm{sup -1}. Additional intensity at {approx} 185-200 cm{sup -1} is interpreted as a set of cluster 'breathing' modes similar to those seen for the FeMo-cofactor. The strength and location of these modes also suggest that the FeMo-co interstitial light atom seen in the crystal structure is already in place in NifB-co. Both the EXAFS and NRVS data for NifX:NifB-co are best simulated using a Fe{sub 6}S{sub 9}X trigonal prism structure analogous to the 6Fe core of FeMo-co, although a 7Fe structure made by capping one trigonal 3S terminus with Fe cannot be ruled out. The results are consistent with the conclusion that the interstitial light atom is already present at an early stage in FeMo-co biosynthesis prior to the incorporation of Mo and R-homocitrate.},
doi = {},
url = {https://www.osti.gov/biblio/953160}, journal = {J. Am. Chem. Soc. 130:5673,2008},
number = 17,
volume = 130,
place = {United States},
year = {Mon May 18 00:00:00 EDT 2009},
month = {Mon May 18 00:00:00 EDT 2009}
}