Deg5 (AT4G18370) is an ATP-independent serine protease and localizes in the luminal side of the thylakoid in chloroplasts. Deg5 and another Deg/HtrA-family protease, Deg8 (AT5G39830) , form a hexamer in the thylakoid lumen and have a synergistic function in the turnover of the D1 protein of damaged photosystem II (PSII) .
