PARENT SESSION
Posters P6A Type II reaction centres: Excited state dynamics and donor side. Abstracts (313-346)

Functional analysis of the PsbP-like protein (SLL1418) in Synechocystissp. PCC 6803. Yasuo Ishikawa^*,1, Wolfgang Schröder¹, Christiane Funk¹, ¹ Department of Biochemistry and Umeå Plant Science Center, Umeå University, Sweden

ABSTRACT- In higher plants, the oxygen-evolving complex (OEC) of Photosystem II is composed of three extrinsic proteins, PsbO, PsbP and PsbQ, and several ions including the Mn-cluster, Ca²⁺. and Cl^-. These proteins attach to Photosystem II on the luminal side of the thylakoid membrane. The PsbP protein, along with the PsbQ protein, are known to act as regulators of the Ca²⁺ and Cl^- concentrations, that are required for effective oxygen evolution in Photosystem II. However, the detailed function of these proteins remains to be elucidated. It has been thought that cyanobacterial cells do not have the PsbP and PsbQ, which are replaced by a 12 kDa protein (PsbU) and a c-type cytochrome (PsbV) in the functions. An recent report, however, shows that PsbQ-like protein is associated with Photosystem II of cyanobacteria, though it has not been verified that the protein has the same functions as PsbQ of higher plants. During investigations of the proteome of the thylakoid lumen from Arabidopsis thaliana and spinach, we elucidated that Arabidopsis contains 2 PsbP proteins and 6 PsbP-domain-protein (16-24kDa), which show partially high similarity to the PsbP protein, in the thylakoid lumen. In the genome of the cyanobacterium Synechocystis sp. PCC 6803, a gene (sll1418) has been identified with a distinct PsbP-domain. Sll1418 codes for a hypothetical protein with a molecular mass of 20.7 kDa and is a homologue to the PsbP-like T215 protein (21.5kDa) from Arabidopsis. In order to study the function of the PsbP-like protein in cyanobacteria, we constructed a mutant lacking sll1418 in Synechocystis 6803. The role of this PsbP-like protein in the photosynthetic apparatus will be discussed.

KEY WORDS: oxygen-evolving complex, photosystem 2, psbp protein