Quality control of Photosystem II: the fate of heat-damaged D1 protein in spinach thylakoids depends on the distribution and action of FtsH proteases and phosphatases in the thylakoids

Abstract

Moderate heat stress (40^οC, 30 min) on spinach thylakoids induced cleavage and aggregation of the D1 protein in Photosystem II. An N-terminal 23-kDa and a C-terminal 9-kDa fragments of the D1 protein, as well as aggregates of the D1 protein were detected by Western blot analysis with specific antibodies. FtsH proteases, which are responsible for cleavage of the heat-damaged D1 protein, were abundant in the stroma thylakoids, but less abundant in the grana or the Photosystem II membranes. Interestingly, FtsH was present even in the Photosystem II core. In the heat-stressed thylakoids, the D1 proteins was dephosphorylated and cleaved, while a large amount of aggregates of phosphorylated D1 protein was detected in the grana and Photosystem II membranes. We suggest that the heat-damaged D1 protein was degraded when dephosphorylated and recognized by FtsH proteases, while the damaged and phosphorylated D1 protein aggregated with the D2 protein and CP43.