Identification of proteolipid from an extremely halophilic archaeon Halobacterium salinarum as an N,N'-dicyclohexyl-carbodiimide binding subunit of ATP synthase

ATP synthesis in an extremely halophilic archaeon, Halobacterium salinarum, was inhibited by N-cyclohexyl-N'-[4-(dimethylamino)-alpha-naphthyl]carbodiimide (NCD-4), a fluorescent analog of N,N'-dicyclohexylcarbodiimide (DCCD). By tracing the fluorescent signal, a hydrophobic 8-kDa protein (proteolipid) was purified from the halobacterial membrane as one of the most DCCD-reactive proteins and its N-terminal amino acid sequence was determined. The gene encoding the proteolipid was found in the region upstream of the genes encoding the two major subunits of halobacterial A-type ATPase [K. Ihara and Y.Mukohata (1991) Arch. Biochem. Biophys. 286, 111-116]. Halobacterial proteolipid was more similar in size to the proteolipid of F-type ATPase than that of V-type ATPase. However, multiple amino acid sequence alignment of proteolipids showed a higher degree of relatedness between V-type and A-type ATPase proteolipids. Together with the recent finding of a triplicate proteolipid encoding gene from the methanogenic archaeon Methanococcus jannaschii [C. J. Bult et al. (1996) Science 273, 1058-1073], proteolipids from archaea seem to have diverse characteristics in comparison with those from eubacteria or from eukaryotes.