Identification of Proteolipid from an Extremely Halophilic ArchaeonHalobacterium salinarumas anN,N′-Dicyclohexyl-carbodiimide Binding Subunit of ATP Synthase

ATP synthesis in an extremely halophilic archaeon,Halobacterium salinarum,was inhibited byN-cyclohexyl-N′-[4-(dimethylamino)-α-naphthyl]carbodiimide (NCD-4), a fluorescent analog ofN,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 archaeonMethanococcus jannaschii[C. J. Bultet al.(1996)Science273, 1058–1073], proteolipids from archaea seem to have diverse characteristics in comparison with those from eubacteria or from eukaryotes.