Auxiliary functions in photosynthesis: the role of the FtsH protease

Oxygenic photosynthesis can be described effectively by using two long-stan ding models: the Z-scheme and the chemiosmotic hypothesis. However, these m odels do not reveal the dynamic nature of the thylakoid membrane and the fo ur major complexes that it binds. The composition of the photosynthetic app aratus is continually changing in response to a range of environmental stim uli. In addition, many photosynthetic components have some of the highest t urnover rates in Nature. Changes in composition and turnover of photosynthe tic components require the degradation of existing and damaged polypeptides and the resynthesis and co-ordinated assembly of new polypeptides and thei r associated cofactors. This is achieved by several auxiliary functions, in cluding proteolysis, protein targeting and the action of molecular chaperon es. Some of the components involved in these functions, such as translocons , chaperones and proteases, have been identified but many of the auxiliary functions of photosynthesis remain uncharacterized. Among the proteases kno wn to be associated with the thylakoids is the zinc metalloprotease FtsH, w hich might also act as a chaperone. Here we provide an overview of the thyl akoid FtsH protease and discuss its role in the maintenance and assembly of the photosynthetic apparatus.