Effects of truncated mutants of the ε subunit of chloroplast ATP synthase on the fast phase of millisecond delayed light emission of chloroplast and its ATP synthesis ability

The e subunit of the chloroplast ATP synthase and the truncated e mutants which lack some amino acid residues from the N-terminus or C-terminus were overexpressed inE. coli. When the e subunit or the truncated e proteins was added to the spinach chloroplast suspension, both the intensity of the fast phase of millisecond delayed light emission (ms-DLE) and the cyclic and noncyclic photophosphorylation activity of chloroplast were enhanced. With an increase in the number of residues deleted from the N-terminus, the enhancement effect of the N-terminal truncated proteins decreased gradually. For the C-terminal truncated proteins, the enhancement effect increased gradually with an increase in the number of residues deleted from the C-terminus. Besides, the ATP synthesis activity of e-deficient membrane reconstituted with the e subunit or the truncatede proteins was compared. The ATP synthesis activity of reconstituted membrane with the N-terminal truncated proteins decreased gradually as the number of residues deleted from the N-terminus increased. For the C-terminal truncated proteins, the ATP synthesis activity of reconstituted membrane increased gradually with an increase in the number of residues deleted from the C-terminus, but was still lower than that of the wild type e protein. These results suggested that: (a) the N-terminal domain of the e subunit of the chloroplast ATP synthase could affect the ATP synthesis activity of ATP synthase by regulating the efficiency of blocking proton leakage of e subunit; and (b) the C-terminal domain of the e subunit of the chloroplast ATP synthase had a subtle function in modulating the ATP synthesis ability of ATP synthase.