STRUCTURAL CHARACTERISATION OF AN IRON-STRESSED PSI SUPERCOMPLEX ISOLATED FROM THERMOSJNECHOCOCCUS ELONGATUS

摘要

The iron-stress induced isiA gene has been identified in several strains of cyanobacteria and is expressed in vitro when the growth medium used is iron depleted. The gene product, IsiA, is similar in sequence to the CP43 protein of photosystem II (PSII), but shorter, lacking ~100 amino acids towards the C-terminus. Due to this, the IsiA protein is sometimes called CP43'. In the cyanobacteriurn Synechocystis PCC 6803 it was demonstrated that iron deficiency induces the formation of an 18-mer IsiA antenna ring around trimeric photosystem I (PSI) (Bibby et al 2001 a). A similar structure was observed in iron-depleted Synechococcus sp PCC 7942 (Boekema et al 2001). Here we investigate the induction of IsiA in Thermosynechococcus elongatus (T. elongatus), a cyanobacteriurn which has yielded high resolution structures of PSI (Jordan et al 2001) and PSII (Zouni et al 2001, Ferreira et al 2004).