Species-specific Differences of the Spectroscopic Properties of P700: ANALYSIS OF THE INFLUENCE OF NON-CONSERVED AMINO ACID RESIDUES BY SITE-DIRECTED MUTAGENESIS OF PHOTOSYSTEM I FROM CHLAMYDOMONAS REINHARDTII

Heike Witt,Enrica Bordignon,Donatella Carbonera,Jan P Dekker,Navassard Karapetyan,Christian Teutloff,Andrew Webber,Wolfgang Lubitz,Eberhard Schlodder

doi:10.1074/jbc.m304776200

Abstract

We applied optical spectroscopy, magnetic resonance techniques, and redox titrations to investigate the properties of the primary electron donor P700 in photosystem I (PS I) core complexes from cyanobacteria (Thermosynechococcus elongatus, Spirulina platensis, and Synechocystis sp. PCC 6803), algae (Chlamydomonas reinhardtii CC2696), and higher plants (Spinacia oleracea). Remarkable species-specific differences of the optical properties of P700 were revealed monitoring the (3P700-P700) and (P700+.-P700) absorbance and CD difference spectra. The main bleaching band in the Qy region differs in peak position and line width for the various species. In cyanobacteria the absorbance of P700 extends more to the red compared with algae and higher plants which is favorable for energy transfer from red core antenna chlorophylls to P700 in cyanobacteria. The amino acids in the environment of P700 are highly conserved with two distinct deviations. In C. reinhardtii a Tyr is found at position PsaB659 instead of a Trp present in all other organisms, whereas in Synechocystis a Phe is found instead of a Trp at the homologous position PsaA679. We constructed several mutants in C. reinhardtii CC2696. Strikingly, no PS I could be detected in the mutant YW B659 indicating steric constraints unique to this organism. In the mutants WA A679 and YA B659 significant changes of the spectral features in the (3P700-P700), the (P700+.-P700) absorbance difference and in the (P700+.-P700) CD difference spectra are induced. The results indicate structural differences among PS I from higher plants, algae, and cyanobacteria and give further insight into specific protein-cofactor interactions contributing to the optical spectra.

Highlights

We applied optical spectroscopy, magnetic resonance techniques, and redox titrations to investigate the properties of the primary electron donor P700 in photosystem I (PS I) core complexes from cyanobacteria
The native and the mutated PS I core complexes WA A679, WH A679, WY A679, YA B659, and YH B659 from C. reinhardtii were purified and spectroscopically characterized together with PS I core complexes from four other species
Mutant Phenotype—As the mutations were introduced into the Chlamydomonas strain CC2696, which in contrast to wild type contains the DS-521 nuclear mutation leading to a deficiency in the Cab proteins and a deletion in psbA causing the loss of PS II, PS I is the main chlorophyll-binding protein

Summary

Introduction

Magnetic resonance techniques, and redox titrations to investigate the properties of the primary electron donor P700 in photosystem I (PS I) core complexes from cyanobacteria The results indicate structural differences among PS I from higher plants, algae, and cyanobacteria and give further insight into specific protein-cofactor interactions contributing to the optical spectra. Photosystem I (PS I) is a multisubunit pigment-protein complex located in the thylakoid membranes of cyanobacteria, algae, and plants that mediates light-induced electron transfer from plastocyanin or cytochrome c6 on the luminal side to ferredoxin on the stromal side The PS I core complexes of all organisms consist of two large subunits, PsaA and PsaB, and at least eight smaller subunits [3]. Only the three-dimensional structure of PS I from T. elongatus is known [8], it is generally assumed that the PS I core complexes, and especially the cofactor arrangement in the reaction center, are similar in all organisms despite the differences described above. This paper is available on line at http://www.jbc.org large subunits are highly conserved and the same holds for the primary photochemistry of the reaction center of PS I, there is a discussion going on that in some species both branches participate in the primary charge separation whereas in other species only the A-branch seems to be active [9, 10]

Methods

Results

Conclusion