Investigation of the in vivo structure of the oxygen-evolving photosystem II (PS II) core complex in Synechococcus elongatus

Abstract

Oxygen evolution is a result of concerted redox reactions in PS II complex having well-organized multisubunit structure. Single unit of PS II complex has been proposed to be associated making a homo-dimeric functional form from electron microscopic observation and radiation target analysis of the oxygen-evolving PS II complex in thylakoid membranes. However, monomeric PS II complexes were also obtained from the size- and shape-analyses of the detergent-solubilized PS II complexes. One of the authors (S.M.) has purified oxygen-evolving PS II core complexes as a dimer from Synechococcus elongatus cells with genetically modified CP43 subunit. We completely determined the in vivo structure of oxygen-evolving PS II complex in this study by comparing the composition of modified CP43 of PS II complexes isolated from thylakoids that had been mixed with various fractions of the thylakoid from untransformed Synechococcus elongatus cells prior to the disintegration of the membranes with dodecyl maltoside. We isolated PS II core complexes that contained Histidine-tagged CP43 without any hybrids with unmodified CP43 from untransformed cells. Thus, we conclude that PS II complexes occur as a dimer before the detergent treatment, i.e. in thylakoid.