Structure of donor side components in photosystem II predicted by computer modelling.

Abstract

Thirty‐one and eleven sequences for the photosystem II reaction centre proteins D1 and D2 respectively, were compared to identify conserved single amino acid residues and regions in the sequences. Both proteins are highly conserved. One important difference is that the lumenal parts of the D1 protein are more conserved than the corresponding parts in the D2 protein. The three‐dimensional structures around the electron donors tyrosineZ and tyrosineD on the oxidizing side of photosystem II have been predicted by computer modelling using the photosynthetic reaction centre from purple bacteria as a framework. In the model the tyrosines occupy two cavities close to the lumenal surface of the membrane. They are symmetrically arranged around the primary donor P680 and the distances between the centre of the tyrosines and the closest Mg ion in P680 are around 14 A. Both tyrosineZ and tyrosineD are suggested to form a hydrogen bond with histidine 190 from the loop connecting helices C and D in the D1 and D2 proteins, respectively. The Mn cluster in the oxygen evolving complex has been localized by using known and estimated distances from the tyrosine radicals. It is suggested that a binding region for the Mn cluster is constituted by the lumenal ends of helices A and B and the loop connecting them in the D1 protein. This part of the D1 protein contains a large number of strictly conserved carboxylic acid residues and histidines which could participate in the Mn binding. There is little probability that the Mn cluster binds on the lumenal surface of the D2 protein.

Thermoluminescence evidence for light‐induced oxidation of tyrosine and histidine residues in manganese‐depleted photosystem II particles

“…Due to its low peak temperature this donor should have a more positive midpoint potential than His*/His or Y,'N,. A computer-predicted threedimensional structure around Y, and Y,, suggested that the tyrosines form hydrogen bonds with nearby histidine residues (His-190) of the Dl and D2 proteins, respectively [27], and a phenylalanine (Phe 186) which is situated between tyrosine and P680, and may be involved in electron transfer between them. The three low-temperature TL bands (TL_,,; TL+, and TL,) observed in manganese-depleted DT-20 particles may COTrespond to the three oxidized aromatic residues (histidine, tyrosine and phenylalanine).…”

Rapid formation of the stable tyrosyl radical in photosystem II

“…This process could be easier with TyrZ than with TyrD, because D1-Glu-189 appears to be (indirectly) associated with a TyrZ deprotonation pathway (47), possibly positioning the proton acceptor for D1- . No equivalent carboxylic acid is conserved in the D2 sequence associated with TyrD, where it is replaced by the acid͞base inactive Phe residue (4,46,(48)(49)(50)(51). Another explanation for TyrZ oxidation being faster than TyrD oxidation at low pH could be the possibility that TyrZ ⅐ has multiple H-bonding partners (for review, see ref.…”

Activation of the silent psbA1 gene in the cyanobacterium Synechocystis sp strain 6803 produces a novel and functional D1 protein.

“…One of these substitutions would exchange the phenylalanine at position 186 for a leucine (Figure 1). Molecular modeling studies have placed Phe-186 in the protein environment around the redox-active tyrosine residue Tyr-161 (Tyrz) (Svensson et al, 1991), and it has been implicated in electron transfer between Tyrz and P680 (Svensson et al, 1990). Mutating Phe-186 to Tyr-186 in Synechocystis sp 6803 abolished oxygen-evolving activity (Maenpaa et al, 1995).…”