Localization and processing of pD1 in Synechocystis PCC6803 membrane fractions

Abstract

Cyanobacteria, belonging to gram-negative bacteria, contain three types of membrane: the outer membrane, the plasma membrane and the thylakoid membrane. A refined study, employing a novel method in isolation of pure plasma and thylakoid membrane fractions, to resolve the membrane structure and composition of S. 6803, has been initiated. Results from this study show traces of PSI and PSII reaction centre core proteins in plasma membrane fraction. Active PSII complexes function in the thylakoid membranes and currently it is not understood why some PSII core proteins additionally exist also in the plasma membrane. The possible involvement of S. 6803 plasma membrane in synthesis of PSII core protein has been investigated by 2D-isolation of pure plasma and thylakoid membrane fractions. Although immunological analysis showed small amounts of PSII proteins D1, D2 and cytb559 in plasma membrane, the precursor form of D1 protein (pD1) was found exclusively in the thylakoid membrane. The relation between PSII complexes in the thylakoid and plasma membrane needs further investigation considering aspects of PSII biogenesis and turnover as well as psbA gene heterogeneity in S. 6803.