Modified Ligands to Fa and Fb in photosystem I. I. Structural constraints for the formation of Iron-Sulfur clusters in free and rebound PsaCThe Journal of Biological Chemistry (1995)
Cysteines 14, 21, 34, 51, or 58 in PsaC of photosystem I (PS I) were replaced with aspartic acid (C21D and C58D), serine (C14S, C34S, and C51S), and alanine (C14A, C34A, and C51A). When free in solution, the C34S and C34A holoproteins contained two S= ground state [4Fe-4S] clusters; all other mutant proteins contained [3Fe-4S] clusters and [4Fe-4S] clusters; in addition, there was evidence in C14S, C51S, C14A, and C51A for high spin (S =) [4Fe-4S] clusters, presumably in the modified site. These findings are consistent with the assignment of C14, C21, C51, and C58, but not C34, as ligands to FAand FB. The [4Fe-4S] clusters in the unmodified sites in C14S, C51S, C14A, and C51A remained highly electronegative, with Em values ranging from −495 to −575 mV. The [3Fe-4S] clusters in the modified sites were driven 400 to 450 mV more oxidizing than the native [4Fe-4S] clusters, with Em values ranging from −98 mV to −171 mV. A C14D/C51D double mutant contains [3Fe-4S] and S= [4Fe-4S] clusters, showing that the 3Cys•1Asp motif is also able to accommodate a low spin cubane. When C34S, C34A, C14S, C51S, C14A, and C51A were rebound to P700-FX cores, electron transfer to FA/FBwas regained, but functional reconstitution has not yet been achieved for C21D, C58D, or C14D/C51D. These data imply that PsaC requires two iron-sulfur clusters to refold, one of which must be a cubane. Since two [4Fe-4S] clusters are found in all reconstituted PS I complexes, the presence of two cubanes in free PsaC may be a necessary precondition for binding to P700-FX cores.
Publication DateNovember 24, 1995
Citation InformationTetemke Mehari, Fengyu Qiao, M. Paul Scott, David F. Nellis, et al.. "Modified Ligands to Fa and Fb in photosystem I. I. Structural constraints for the formation of Iron-Sulfur clusters in free and rebound PsaC" The Journal of Biological Chemistry Vol. 270 Iss. 47 (1995) p. 28108 - 28117
Available at: http://works.bepress.com/paul-scott/50/