TY - JOUR
T1 - 13C Electron Nuclear Double Resonance Spectroscopy Shows Acetyl-CoA Synthase Binds Two Substrate CO in Multiple Binding Modes and Reveals the Importance of a CO-Binding "alcove"
AU - James, Christopher D.
AU - Wiley, Seth
AU - Ragsdale, Stephen W.
AU - Hoffman, Brian M.
N1 - Funding Information:
This work was supported by the NSF (MCB-1908587, BMH) and the NIH (R37 GM039451, SWR). We are grateful to Drs. Catherine Drennan, Steven Cohen, and Ritimukta Sarangi for discussions of the structural implications of these C-ENDOR results. 13
Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/9/9
Y1 - 2020/9/9
N2 - EPR and Electron Nuclear Double Resonance spectroscopies here characterize CO binding to the active-site A cluster of wild-type (WT) Acetyl-CoA Synthase (ACS) and two variants, F229W and F229A. The A-cluster binds CO to a proximal Ni (Nip) that bridges a [4Fe-4S] cluster and a distal Nid. An alcove seen in the ACS crystal structure near the A-cluster, defined by hydrophobic residues including F229, forms a cage surrounding a Xe mimic of CO. Previously, we only knew WT ACS bound a single CO to form the Ared-CO intermediate, containing Nip(I)-CO with CO located on the axis of the dz2 odd-electron orbital (g⊥ > g∥ ∼2). Here, the two-dimensional field-frequency pattern of 2K-35 GHz 13C-ENDOR spectra collected across the Ared-CO EPR envelope reveals a second CO bound in the dz2 orbital's equatorial plane. This WT A-cluster conformer dominates the nearly conservative F229W variant, but 13C-ENDOR reveals a minority "A"conformation with (g∥ > g⊥ ∼2) characteristic of a "cloverleaf"(e.g., dx2-y2) odd-electron orbital, with Nip binding two, apparently "in-plane"CO. Disruption of the alcove through introduction of the smaller alanine residue in the F229A variant diminishes conversion to Ni(I) ∼10-fold and introduces extensive cluster flexibility. 13C-ENDOR shows the F229A cluster is mostly (60%) in the "A"conformation but with ∼20% each of the WT conformer and an "O"state in which dz2 Nip(I) (g⊥ > g∥ ∼2) surprisingly lacks CO. This paper thus demonstrates the importance of an intact alcove in forming and stabilizing the Ni(I)-CO intermediate in the Wood-Ljungdahl pathway of anaerobic CO and CO2 fixation.
AB - EPR and Electron Nuclear Double Resonance spectroscopies here characterize CO binding to the active-site A cluster of wild-type (WT) Acetyl-CoA Synthase (ACS) and two variants, F229W and F229A. The A-cluster binds CO to a proximal Ni (Nip) that bridges a [4Fe-4S] cluster and a distal Nid. An alcove seen in the ACS crystal structure near the A-cluster, defined by hydrophobic residues including F229, forms a cage surrounding a Xe mimic of CO. Previously, we only knew WT ACS bound a single CO to form the Ared-CO intermediate, containing Nip(I)-CO with CO located on the axis of the dz2 odd-electron orbital (g⊥ > g∥ ∼2). Here, the two-dimensional field-frequency pattern of 2K-35 GHz 13C-ENDOR spectra collected across the Ared-CO EPR envelope reveals a second CO bound in the dz2 orbital's equatorial plane. This WT A-cluster conformer dominates the nearly conservative F229W variant, but 13C-ENDOR reveals a minority "A"conformation with (g∥ > g⊥ ∼2) characteristic of a "cloverleaf"(e.g., dx2-y2) odd-electron orbital, with Nip binding two, apparently "in-plane"CO. Disruption of the alcove through introduction of the smaller alanine residue in the F229A variant diminishes conversion to Ni(I) ∼10-fold and introduces extensive cluster flexibility. 13C-ENDOR shows the F229A cluster is mostly (60%) in the "A"conformation but with ∼20% each of the WT conformer and an "O"state in which dz2 Nip(I) (g⊥ > g∥ ∼2) surprisingly lacks CO. This paper thus demonstrates the importance of an intact alcove in forming and stabilizing the Ni(I)-CO intermediate in the Wood-Ljungdahl pathway of anaerobic CO and CO2 fixation.
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U2 - 10.1021/jacs.0c05950
DO - 10.1021/jacs.0c05950
M3 - Article
C2 - 32786751
AN - SCOPUS:85090613406
VL - 142
SP - 15362
EP - 15370
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 36
ER -