TY - JOUR
T1 - The bound iron-sulfur clusters of Type-I homodimeric reaction centers
AU - Romberger, Steven P.
AU - Golbeck, John H.
N1 - Funding Information:
Acknowledgments This work was funded by a grant from the U.S. Department of Energy (DE-FG02-08ER20314). The authors thank Dr. Kevin Redding for identifying the presence of HM1_0860 in the heliobacterial genome and Dr. Scott Showalter for pointing out the presence of multiple PxxP motifs and their likelihood to interact with SH3 domains.
PY - 2010/6
Y1 - 2010/6
N2 - The hallmark of a Type-I photosynthetic reaction center (RC) is the presence of three [4Fe-4S]2+/1+ clusters, named FX, FA, and FB that act as terminal electron acceptors. Their function is to increase the distance, and hence the lifetime, of the initial charge-separated state so that diffusion-mediated processes, such as the reduction of ferredoxin, can occur. Type-I homodimeric RCs, such as those found in heliobacteria, green-sulfur bacteria, and Candidatus Chloracidobacterium thermophilum, are less well understood than Photosystem I, the prototypical Type-I heterodimeric RC found in cyanobacteria and plants. Here, we review recent progress that has been made in elucidating the spectroscopic and biochemical properties of the bound Fe/S clusters and their cognate proteins in homodimeric Type-I RCs. In Heliobacterium modesticaldum, the identification and characterization of two loosely bound polypeptides, PshBI and PshBII that harbor the FA and FB clusters threatens to break the long-accepted assumption that Type-I RCs harbor one tightly bound FA/FB-containing protein. Additionally, the detection of the FX cluster in S = 1/2 and S = 3/2 ground spin states has resolved the long-standing issue of its missing EPR spectrum. In Chlorobaculum tepidum, the focus is on the biochemical properties of the unusual extrinsic Fe/S protein, PscB, which is readily dissociable from the RC core. The C-terminal domain of PscB is constructed as a bacterial ferredoxin, harboring the FA and FB clusters, but the N-terminal domain contains a number of PxxP motifs and is rich in Lys, Pro, and Ala residues, features characteristic of proteins that interact with SH3 domains. Little is known about Candidatus Chloracidobacterium thermophilum except that the photosynthetic RC is predicted to be a Type-I homodimer with an FX-binding site. These findings are placed in a context that promises to unify the acceptor side of homodimeric Type-I RCs in prokaryotic phototrophs.
AB - The hallmark of a Type-I photosynthetic reaction center (RC) is the presence of three [4Fe-4S]2+/1+ clusters, named FX, FA, and FB that act as terminal electron acceptors. Their function is to increase the distance, and hence the lifetime, of the initial charge-separated state so that diffusion-mediated processes, such as the reduction of ferredoxin, can occur. Type-I homodimeric RCs, such as those found in heliobacteria, green-sulfur bacteria, and Candidatus Chloracidobacterium thermophilum, are less well understood than Photosystem I, the prototypical Type-I heterodimeric RC found in cyanobacteria and plants. Here, we review recent progress that has been made in elucidating the spectroscopic and biochemical properties of the bound Fe/S clusters and their cognate proteins in homodimeric Type-I RCs. In Heliobacterium modesticaldum, the identification and characterization of two loosely bound polypeptides, PshBI and PshBII that harbor the FA and FB clusters threatens to break the long-accepted assumption that Type-I RCs harbor one tightly bound FA/FB-containing protein. Additionally, the detection of the FX cluster in S = 1/2 and S = 3/2 ground spin states has resolved the long-standing issue of its missing EPR spectrum. In Chlorobaculum tepidum, the focus is on the biochemical properties of the unusual extrinsic Fe/S protein, PscB, which is readily dissociable from the RC core. The C-terminal domain of PscB is constructed as a bacterial ferredoxin, harboring the FA and FB clusters, but the N-terminal domain contains a number of PxxP motifs and is rich in Lys, Pro, and Ala residues, features characteristic of proteins that interact with SH3 domains. Little is known about Candidatus Chloracidobacterium thermophilum except that the photosynthetic RC is predicted to be a Type-I homodimer with an FX-binding site. These findings are placed in a context that promises to unify the acceptor side of homodimeric Type-I RCs in prokaryotic phototrophs.
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U2 - 10.1007/s11120-010-9543-y
DO - 10.1007/s11120-010-9543-y
M3 - Review article
C2 - 20405215
AN - SCOPUS:77953646649
SN - 0166-8595
VL - 104
SP - 333
EP - 346
JO - Photosynthesis research
JF - Photosynthesis research
IS - 2
ER -