Difference between Biological Activities and Secondary Structures of Expression Product of atpE Gene from Broad Bean...

The chloroplast atpE genes from broad bean and maize were overexpressed in E.coli, respectively. After proper refolding and purification, two types of epsilon-subunit proteins with biological activity were obtained. When reconstituted with CF(1)(-epsilon)from different chloroplast ATPase, the effects of the reconstructed epsilon-subunit protein of maize CF(1) to the Ca(2+)-ATPase activity of epsilon-deficient CF(1) and to the proton leakage through CF(0) were markedly stronger than that of broad bean CF(1). It was also observed that the enhancing effect of maize epsilon-subunit protein to the chloroplast photophosphorylation activity was greater than that of broad bean epsilon-subunit protein. The results indicate that (1)the inhibition of epsilon-subunit is closely related to the its affinity with other parts of CF(1) (2)both functions of epsilon-subunit as inhibitor of ATPase and as proton pathway are closely linked. The circular dichroism was performed to show the differences in their secondary structure of these epsilon-subunit proteins based on the deduced primary sequences. Unconstrained analysis of the CD spectrum for the maize epsilon-subunit protein gave 22.6% alpha-helix, 30.6% beta-sheet, 9.3% beta-turn, and 37.7% unordered structure and 31.4%alpha-helix, 22.3% beta-sheet, 13.8% beta-turn, and 32.4% unordered structure for the epsilon-subunit from broad bean.