title: Correlation of the cytochrome c (550) content of cyanobacterial Photosystem II with the EPR properties of the oxygen-evolving complex.
abstract: The Mn(4) cluster of PS II advances through a series of oxidation states (S states) that catalyze the breakdown of water to dioxygen in the oxygen-evolving complex. The present study describes the engineering and purification of highly active PS II complexes from mesophilic His-tagged Synechocystis PCC 6803 and purification of PS II core complexes from thermophilic wild-type Synechococcus lividus with high levels of the extrinsic polypeptide, cytochrome c (550). The g = 4.1 S(2) state EPR signal, previously not characterized in untreated cyanobacterial PS II, is detected in high yields in these PS II preparations. We present a complete characterization of the g = 4.1 state in cyanobacterial His-tagged Synechocystis PCC 6803 PS II and S. lividus PS II. Also presented are a determination of the stoichiometry of cytochrome c (550) bound to His-tagged Synechocystis PCC 6803 PS II and analytical ultracentrifugation results which indicate that cytochrome c (550) is a monomer in solution. The temperature-dependent multiline to g = 4.1 EPR signal conversion observed for the S(2) state in cyanobacterial PS II with high cytochrome c (550) content is very similar to that previously found for spinach PS II. In spinach PS II, the formation of the S(2) state g = 4.1 EPR signal has been found to correlate with the binding of the extrinsic 17 and 23 kDa polypeptides. The finding of a similar correlation in cyanobacterial PS II with the binding of cytochrome c (550) suggests a functional homology between cytochrome c (550) and the 17 and 23 kDa extrinsic proteins of spinach PS II.
authors.affiliation: Department of Chemistry, Yale University, New Haven, CT, 06520-8107, USA, gary.brudvig@yale.edu.
authors.forename: K V
authors.initials: KV
authors.lastname: Lakshmi
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Reifler
authors.forename: Dexter A
authors.initials: DA
authors.lastname: Chisholm
authors.forename: Jamie Y
authors.initials: JY
authors.lastname: Wang
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Diner
authors.forename: Gary W
authors.initials: GW
authors.lastname: Brudvig