Identification of a protease involved in the repair of photosystem two in Synechocystis 6803

Abstract

Protein folding has been at the forefront of molecular cell biology research for a number of years. Integral membrane proteins have, however, eluded detailed molecular level study until recently. One reason is the often apparently insurmountable problem of mimicking the natural membrane bilayer with lipid or detergent mixtures. There is, however, a large body of information on lipid properties and in particular on phosphatidylcholine and phosphatidylethanolamine lipids which are common to many biological membranes. We have exploited this knowledge to design efficient in vitro lipid-bilayer folding systems for membrane proteins. Bacteriorhodopsin has been used as a model system for our initial studies, and we have shown that a ratelimiting apoprotein folding step and the overall folding efficiency appear to be controlled by particular properties of the lipid bilayer. The properties of interest are the stored curvature elastic energy within the bilayer and the lateral pressure that the lipid chains exert on their neighbouring folding protein. These are generic properties of the bilayer that can be achieved with simple mixtures of many types of biological lipids and seem to be important in vivo. 4 The first green: assembly of quantum traps in higher plantIf not strictly controlled, chlorophyll may work as a hazardous photooxidant in the oxigenic surrounding of the plant cell. Biogenesis of functional chlorophyll bearing photosynthetic quantum traps is therefore a strictly regulated matter throughout in nature. Plants grown in complete darkness develop a light regulated quantum trap, protochlorophyllide oxidoreductase (POR), and already start structural biogenesis of photosynthetic quantum traps. POR regulates phototransformation of the chlorophyll precursor educt and the availability of the product chlorophyllide for final esterification with geranylgeranylpyrophosphate by Chlorophyll-synthase. Chlorophyll then strictly controls functional biogenesis of photosynthetic reaction centers, core complexes and light harvesting complexes. Etioplasts isolated from barley seedlings are used as a model to demonstrate by time resolved spectroscopy and electrophoretic techniques, how photoreduction, esterification and photosystem assembly are coordinated and regulated. The high resolution obtained for separation of membrane proteins now enables us to investigate the protein protein interactions of assembly regulators during photosystem biogenesis.Genes of the HSP70 family are induced by light. In Chlamydomonas reinhardtii, light induction led to a partial protection of photosystem I1 against photoinhibition. Underexpression of a chloroplast-localized HSP70 protein caused an increased light sensitivity of photosystem 11, whereas its overexpression had a protective effect. Fluorescence measurements and data on the turnover of photosystem I1 core components suggest that this HSP70 may function both in protection and regeneration of photosystem 11. This concept is supported by fractionation studies in which HSP70 was found associat...