Replacement of tyrosine D with phenylalanine affects the normal proton transfer pathways for the reduction of P680+ in oxygen-evolving photosystem II particles from Chlamydomonas.
We have probed the electrostatics of P680(+) reduction in oxygenic photosynthesis using histidine-tagged and histidine-tagged Y(D)-less Photosystem II cores. We make two main observations: (i) that His-tagged Chlamydomonas cores show kinetics which are essentially identical to those of Photosystem II enriched thylakoid membranes from spinach; (ii) that the microsecond kinetics, previously shown to be proton/hydrogen transfer limited [Schilstra et al. (1998) Biochemistry 37, 3974-3981], are significantly different in Y(D)-less Chlamydomonas particles when compared with both the His-tagged Chlamydomonas particles and the spinach membranes. The oscillatory nature of the kinetics in both Chlamydomonas samples is normal, indicating that S-state cycling is unaffected by either the histidine-tagging or the replacement of tyrosine D with phenylalanine. We propose that the effects on the proton-coupled electron transfers of P680(+) reduction in the absence of Y(D) are likely to be due to pK shifts of residues in a hydrogen-bonded network of amino acids in the vicinity of Y(Z). Tyrosine D is 35 A from Y(Z) and yet has a significant influence on proton-coupled electron transfer events in the vicinity of Y(Z). This finding emphasizes the delicacy of the proton balance that Photosystem II has to achieve during the water splitting process.
Jeans
C
C
Molecular Dynamics Group, Department of Chemistry, Imperial College, London SW7 2AY, UK.
Schilstra
M J
MJ
Ray
N
N
Husain
S
S
Minagawa
J
J
Nugent
J H A
JH
Klug
D R
DR
D020418:Algal Proteins; D019943:Amino Acid Substitution / Q000235:genetics*; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000737:chemistry* / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy; D004735:Energy Transfer; D005609:Free Radicals / Q000737:chemistry; D007700:Kinetics; D016254:Mutagenesis, Insertional; D010084:Oxidation-Reduction; D010649:Phenylalanine / Q000737:chemistry* / Q000235:genetics; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics; D011522:Protons; D018724:Spinacia oleracea / Q000737:chemistry; D055672:Static Electricity; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000235:genetics
D020418:Algal Proteins; D005609:Free Radicals; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D011522:Protons; C052389:oxygen-evolving enhancer protein 1, plant; C066447:tyrosyl radical Y(D); D014443:Tyrosine; D010649:Phenylalanine