title: Negatively charged residues in the H loop of PsaB subunit in Photosystem I from Synechocystis sp. PCC 6803 appear to be responsible for electrostatic repulsions with plastocyanin*.
abstract: Wild-type plastocyanin from the cyanobacterium Synechocystis sp. PCC 6803 does not form any kinetically detectable transient complex with Photosystem I (PS I) during electron transfer, but the D44R/D47R double mutant of copper protein does [De la Cerda et al. (1997) Biochemistry 36: 10125-10130]. To identify the PS I component that is involved in the complex formation with the D44R/D47R plastocyanin, the kinetic efficiency of several PS I mutants, including a PsaF-PsaJ-less PS I and deletion mutants in the lumenal H and J loops of PsaB, were analyzed by laser flash absorption spectroscopy. The experimental data herein suggest that some of the negative charges at the H loop of PsaB are involved in electrostatic repulsions with mutant plastocyanin. Mutations in the J loop demonstrate that this region of PsaB is also critical. The interaction site of PS I is thus not as defined as first expected but much broader, thereby revealing how complex the evolution of intermolecular electron transfer mechanisms in photosynthesis has been.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Centro Isla de la Cartuja, Américo Vespucio s/n, 41092, Sevilla, Spain.
authors.forename: J A
authors.initials: JA
authors.lastname: Navarro
authors.forename: M
authors.initials: M
authors.lastname: Hervás
authors.forename: J
authors.initials: J
authors.lastname: Sun
authors.forename: B
authors.initials: B
authors.lastname: De la Cerda
authors.forename: P R
authors.initials: PR
authors.lastname: Chitnis
authors.forename: M A
authors.initials: MA
authors.lastname: De la Rosa