Mutational analysis of the structure and biogenesis of the photosystem I reaction center in the cyanobacterium Synechocystis sp. PCC 6803

Authors

Lawrence B. Smart, Michigan State University
Patrick V. Warren, University of Nebraska-Lincoln
John H. Golbeck, University of Nebraska - Lincoln
Lee McIntosh, Michigan State University

Document Type

Article

Date of this Version

1993

Comments

Published in Proc. Natl. Acad. Sci. USA Vol. 90, pp. 1132-1136, February 1993. Used by Permission.

Abstract

We have utilized the unicellular cyanobacterium Synechocystis sp. PCC 6803 to incorporate site-directed amino acid substitutions into the photosystemn I (PSI) reactioncenter protein PsaB. A cysteine residue (position 565 of PsaB) proposed to serve as a ligand to the [4Fe-4S] center F_x was changed to serine, histidine, and aspartate. These three mutants- C565S, C565H, and C565D-all exhibited greatly reduced accumulation of PSI reaction-center proteins and failed to grow autotrophically, indicating that this cysteine most likely does coordinate F_x, which is crucial for PSI biogenesis. Interestingly, the strain C565S accumulated significantly more PSI than the other two cysteine mutants and displayed photoreduction of the [4Fe-4S] terminal electron acceptors F_A and F_B. Mutations were also introduced into a leucine zipper motif of PsaB, proposed to participate in reaction-center dimerization. The mutants L522V, L536M, and L522V/L536M all exhibited wild-type characteristics and grew autotrophically, whereas the L522P mutation prevented PSI accumulation. These data do not provide support for a major structural role of the leucine zipper in reaction-center dimerization or in assembly of F_x. However, the amino acid substitutions incorporated were conservative and might not have perturbed the leucine zipper.