TY - JOUR
T1 - A comparative analysis of the spin state distribution of in vitro and in vivo mutants of PsaC. A biochemical argument for the sequence of electron transfer in Photosystem I as F(X) → F(A) → F(B) → ferredoxin/flavodoxin
AU - Golbeck, John H.
N1 - Funding Information:
I gratefully acknowledge my collaborators: Don Bry-ant and Jindong Zhao (Penn State University) for engineering the alanine, serine and aspartate series of in vitro mutants of PsaC as well as the expression of PsaC, PsaD and PsaE in E. coli; Ms Vicki Styrewald (Penn State University) for engineering the glycine series of in vitro mutants of PsaC; Lee McIntosh and Jianping Yu (Michigan State University) for carrying out the in vivo mutagenesis of PsaC in Synechocystis sp. PCC 6803, Kevin Parrett and Tetemke Mehari (Portland State University) for developing the methods for isolating P700-FX cores and reconstituting P700-FA/FB complexes; Lian Yu (University of Nebraska) for reconstituting and studying the spectroscopic properties of the in vitro mutants of PsaC; Yean-Sung Jung (University of Nebraska) for determining the spectroscopic properties of the in vivo mutants of PsaC; and Fan Yang (University of Nebraska) for determining the properties of the aryl thiolate ligands to PsaC and the properties of the monoFB PsaC. I am endebted to John Biggins and Chou Hong-Chen (Brown University) for making available the genes for the modified 4-α-helical bundle and the monoFB PsaC protein, and I thank Richard Malkin (University of California, Berkeley) for permission to reproduce Figures 1A and 14A, and Dietmar Stehlik (Freie Universität, Berlin) for permission to reproduce and modify Figure 15. Finally, I thank Don Bryant and Art Van der Est (Freie Universität, Berlin) for a detailed reading and critical evaluation of the manuscript. Funding for this work was provided by the National Science Foundation, Molecular Biophysics Division (MCB-972366).
PY - 1999
Y1 - 1999
N2 - The EPR properties of in vivo and in vitro C14X-PS I and C51X-PS I (X = D, S, A or G) mutants of PsaC are compared in an attempt to extract information about electron transfer not contained in any one of these studies in isolation. This analysis indicates that 1) sulfur from an external 'rescue thiolate' is preferred over oxygen from an aspartate or serine replacement amino acid as a ligand to the F(A) and F(B) iron-sulfur clusters; 2) the inherent spectroscopic symmetry in the F(A) and F(B) clusters of unbound PsaC is lost when PsaC is docked to its site on the PsaA/PsaB heterodimer; 3) the bound 'rescue thiolate' ligand in the modified site of the F(A) cluster, but not the F(B), cluster is displaced when PsaC is docked to its site on the PsaA/PsaB heterodimer; 4) the free energy of binding PsaC to the PsaA/PsaB heterodimer drives the otherwise-unfavorable ligand replacement in the F(A) site. These and other findings argue that the substitute ligands support a [4Fe-4S] cluster at the modified site, but the cluster is in either a ground spin state of S ≥ 3/2 or S = 1/2 depending on the chemical identity of the ligand, on whether PsaC is unbound or bound, and on the reduction state of the cluster in the unmodified site. By a comparative analysis of the spin state distribution of the in vivo and in vitro C14X-PS I and C51X-PS I (X = D, S, A or G) mutants, and with knowledge from the X-ray crystal structure that PsaC is bound asymmetrically to the PSI reaction center, an independent case is made that PsaC is oriented so that the F(A) cluster is proximal to F(X) and the F(B) cluster is distal to F(X). These results are compared and contrasted with the results of in vivo mutagenesis studies of PsaC in Anabaena variabilis ATCC 29413 and in Chlamydomonas reinhardtii. In all cases, the primary data can be interpreted to support the sequence of electron transfer as F(X) → F(A) → F(B) → ferredoxin.
AB - The EPR properties of in vivo and in vitro C14X-PS I and C51X-PS I (X = D, S, A or G) mutants of PsaC are compared in an attempt to extract information about electron transfer not contained in any one of these studies in isolation. This analysis indicates that 1) sulfur from an external 'rescue thiolate' is preferred over oxygen from an aspartate or serine replacement amino acid as a ligand to the F(A) and F(B) iron-sulfur clusters; 2) the inherent spectroscopic symmetry in the F(A) and F(B) clusters of unbound PsaC is lost when PsaC is docked to its site on the PsaA/PsaB heterodimer; 3) the bound 'rescue thiolate' ligand in the modified site of the F(A) cluster, but not the F(B), cluster is displaced when PsaC is docked to its site on the PsaA/PsaB heterodimer; 4) the free energy of binding PsaC to the PsaA/PsaB heterodimer drives the otherwise-unfavorable ligand replacement in the F(A) site. These and other findings argue that the substitute ligands support a [4Fe-4S] cluster at the modified site, but the cluster is in either a ground spin state of S ≥ 3/2 or S = 1/2 depending on the chemical identity of the ligand, on whether PsaC is unbound or bound, and on the reduction state of the cluster in the unmodified site. By a comparative analysis of the spin state distribution of the in vivo and in vitro C14X-PS I and C51X-PS I (X = D, S, A or G) mutants, and with knowledge from the X-ray crystal structure that PsaC is bound asymmetrically to the PSI reaction center, an independent case is made that PsaC is oriented so that the F(A) cluster is proximal to F(X) and the F(B) cluster is distal to F(X). These results are compared and contrasted with the results of in vivo mutagenesis studies of PsaC in Anabaena variabilis ATCC 29413 and in Chlamydomonas reinhardtii. In all cases, the primary data can be interpreted to support the sequence of electron transfer as F(X) → F(A) → F(B) → ferredoxin.
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U2 - 10.1023/A:1006281802710
DO - 10.1023/A:1006281802710
M3 - Review article
AN - SCOPUS:0032696532
SN - 0166-8595
VL - 61
SP - 107
EP - 144
JO - Photosynthesis research
JF - Photosynthesis research
IS - 2
ER -