Abstract
There are three D1 genes in a thermophilic cyanobacterium Thermosynecococcus elongatus genome. D1:1 gene constitutively expresses under the normal cultivation conditions, whereas the expression of D1:3 gene is induced by high light and UV. The amino acid sequences of D1:1 and D1:3 differ by 21 residues. To investigate the effects on molecular structure and function of these different amino acid residues, the energetic properties of isolated D1:1-PSII complex and D1:3-PSII complex were analysed. O2 evolution was consistently found higher in D1:3-PSII than in D1:1-PSII. The S3QB- charge recombination in D1:3-PSII, experimented by thermoluminescence, occurred at higher temperature than in D1:1-PSII whereas the peak temperature of S2QA- (+DCMU) was less affected. Differences close to the QB site in D1:1 and D1:3 are proposed to modify the interactions with one lipid and the QB site. In plants and most of cyanobacteria, the amino acid D1-130 is a Glu which is H-bonded to PheoD1. In T. elongatus, although D1:3-130 is Glu, the amino acid of D1:1 is Gln. The Pheo/Pheo- redox potential by spectroelectrochemical measurements is shown to be 17 mV more negative in D1:1-PSII than D1:3-PSII.
