Some filamentous cyanobacteria form heterocysts under conditions lacking combined nitrogen for nitrogen fixation. Photosystem II is removed from heterocyst during the process of cell differentiation. Here, we demonstrate that Alr3815 is a protease that is capable of degrading D1 protein of photosystem II. Strain-322, which lacks alr3815, is impaired in nitrogen fixation in air because some oxygen evolving activity is retained in its heterocysts. Our results also suggest that calcium may play a regulatory role in D1 degradation during heterocyst differentiation.
Yang GuoHua; Hu Bin; Zhao JinDong.Specific degradation of photosystem II D1 protein by a protease (Alr3815) in heterocysts of the cyanobacterium Anabaena sp PCC7120,CHINESE SCIENCE BULLETIN,2011,56(11):1068-1070