title: The bound iron-sulfur clusters of type-I homodimeric reaction centers.
abstract: The hallmark of a Type-I photosynthetic reaction center (RC) is the presence of three [4Fe-4S](2+/1+) clusters, named F(X), F(A), and F(B) 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 F(A) and F(B) clusters threatens to break the long-accepted assumption that Type-I RCs harbor one tightly bound F(A)/F(B)-containing protein. Additionally, the detection of the F(X) 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 F(A) and F(B) 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 F(X)-binding site. These findings are placed in a context that promises to unify the acceptor side of homodimeric Type-I RCs in prokaryotic phototrophs.
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Steven P
authors.initials: SP
authors.lastname: Romberger
authors.forename: John H
authors.initials: JH
authors.lastname: Golbeck
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization
chemical_list: D001426:Bacterial Proteins; D007506:Iron-Sulfur Proteins; D045322:Photosynthetic Reaction Center Complex Proteins
references.citation: Biochemistry. 1995 Oct 3;34(39):12761-7
references.pmid: 7548030
references.citation: Biochemistry. 1999 Sep 14;38(37):12124-37
references.pmid: 10508417
references.citation: Biophys J. 2001 Sep;81(3):1208-19
references.pmid: 11509338
references.citation: Cell Mol Life Sci. 2009 Apr;66(7):1257-70
references.pmid: 19132290
references.citation: J Biol Chem. 1973 Jun 10;248(11):3987-96
references.pmid: 4708097
references.citation: Curr Opin Chem Biol. 1999 Apr;3(2):152-7
references.pmid: 10226040
references.citation: Curr Opin Microbiol. 2003 Apr;6(2):181-5
references.pmid: 12732309
references.citation: Sci STKE. 2003 May 13;2003(182):pe17
references.pmid: 12746546
references.citation: Proc Natl Acad Sci U S A. 1992 Sep 1;89(17):8135-9
references.pmid: 1518838
references.citation: Biochim Biophys Acta. 1992 Jul 17;1101(2):154-6
references.pmid: 1633181
references.citation: Photosynth Res. 2005;85(1):51-72
references.pmid: 15977059
references.citation: Photosynth Res. 1996 Oct;50(1):71-7
references.pmid: 24271823
references.citation: Annu Rev Biochem. 2009;78:701-22
references.pmid: 19489731
references.citation: Biochim Biophys Acta. 2008 Dec;1777(12):1535-44
references.pmid: 18835244
references.citation: Science. 2007 Jul 27;317(5837):523-6
references.pmid: 17656724
references.citation: Proc Natl Acad Sci U S A. 1998 Dec 8;95(25):14851-6
references.pmid: 9843979
references.citation: Chem Rev. 2007 Oct;107(10):4273-303
references.pmid: 17850165
references.citation: Photosynth Res. 2009 May;100(2):79-87
references.pmid: 19437128
references.citation: J Biol Chem. 1998 Jul 24;273(30):18778-83
references.pmid: 9668051
references.citation: Ann N Y Acad Sci. 1994 Jul 29;726:215-22
references.pmid: 8092678
references.citation: FEBS Lett. 1977 Mar 15;75(1):33-6
references.pmid: 192591
references.citation: Photosynth Res. 2000;63(3):269-80
references.pmid: 16228437
references.citation: Biochemistry. 2006 May 23;45(20):6306-16
references.pmid: 16700542
references.citation: Nature. 2001 Jun 21;411(6840):909-17
references.pmid: 11418848
references.citation: Biochim Biophys Acta. 1998 Dec 1;1409(2):87-98
references.pmid: 9838060
references.citation: Photosynth Res. 2000;64(1):27-39
references.pmid: 16228441
references.citation: Trends Biochem Sci. 1997 Jan;22(1):3-6
references.pmid: 9020582
references.citation: Proc Natl Acad Sci U S A. 1993 Aug 1;90(15):7124-8
references.pmid: 8346224
references.citation: Proc Natl Acad Sci U S A. 1985 Oct;82(20):6865-8
references.pmid: 16593617
references.citation: Biochemistry. 2009 Jun 16;48(23):5405-16
references.pmid: 19432395
references.citation: J Mol Biol. 1999 Jul 23;290(4):851-8
references.pmid: 10398586
references.citation: J Biol Inorg Chem. 2000 Feb;5(1):2-15
references.pmid: 10766431
references.citation: Biochemistry. 1990 Dec 18;29(50):11079-88
references.pmid: 2176893
references.citation: Biochemistry. 2006 May 30;45(21):6756-64
references.pmid: 16716087
references.citation: Philos Trans R Soc Lond B Biol Sci. 2003 Jan 29;358(1429):231-43
references.pmid: 12594931
references.citation: Annu Rev Microbiol. 1995;49:335-66
references.pmid: 8561464
references.citation: Biochemistry. 1989 Dec 26;28(26):9898-904
references.pmid: 2620065
references.citation: Photosynth Res. 1994 Feb;39(2):163-74
references.pmid: 24311068
references.citation: Biochemistry. 1995 Oct 10;34(40):13091-7
references.pmid: 7548069
references.citation: Eur J Biochem. 1997 Mar 1;244(2):454-61
references.pmid: 9119012
references.citation: J Biol Chem. 1992 Oct 15;267(29):21139-45
references.pmid: 1383218
references.citation: Biochim Biophys Acta. 2001 Oct 30;1507(1-3):139-60
references.pmid: 11687212
references.citation: Biochim Biophys Acta. 1989 Feb 28;973(2):324-32
references.pmid: 2537101
references.citation: Biochemistry. 2005 Jul 26;44(29):9950-60
references.pmid: 16026168
references.citation: Biochemistry. 1992 Mar 10;31(9):2608-14
references.pmid: 1312353
references.citation: FEBS Lett. 1995 May 22;365(1):30-4
references.pmid: 7774710
references.citation: Biochemistry. 1990 Apr 24;29(16):3834-42
references.pmid: 2162198
references.citation: Photosynth Res. 1994 Jul;41(1):105-14
references.pmid: 24310017
references.citation: Nature. 2007 May 3;447(7140):58-63
references.pmid: 17476261
references.citation: J Bacteriol. 2008 Jul;190(13):4687-96
references.pmid: 18441057
references.citation: Photosynth Res. 1994 Jul;41(1):115-23
references.pmid: 11539856
references.citation: Photosynth Res. 1993 Oct;38(1):111-4
references.pmid: 24317836
references.citation: Photosynth Res. 1992 Apr;32(1):11-22
references.pmid: 24408151
references.citation: Biochim Biophys Acta. 2001 Oct 30;1507(1-3):260-77
references.pmid: 11687219
references.citation: Biophys J. 2000 Jun;78(6):3160-9
references.pmid: 10827992
references.citation: Biochemistry. 1995 Jul 25;34(29):9617-24
references.pmid: 7626630
references.citation: Biochim Biophys Acta. 1976 May 14;430(2):244-52
references.pmid: 6060
references.citation: Science. 1997 Aug 1;277(5326):653-9
references.pmid: 9235882
references.citation: Biochemistry. 1992 May 5;31(17):4354-63
references.pmid: 1314661
references.citation: Curr Opin Struct Biol. 2003 Aug;13(4):418-23
references.pmid: 12948771
references.citation: Biochemistry. 2007 Mar 6;46(9):2530-6
references.pmid: 17291010
references.citation: Biochemistry. 1998 Jul 28;37(30):10792-7
references.pmid: 9692969
references.citation: J Biol Chem. 2004 Dec 3;279(49):51122-30
references.pmid: 15371432
references.citation: J Biol Chem. 1985 Sep 15;260(20):11160-73
references.pmid: 2993304
references.citation: J Mol Biol. 2003 Mar 28;327(3):671-97
references.pmid: 12634061