Structure of a 16 kDa integral membrane protein that has identity to the putative proton channel of the vacuolar H+-ATPase

A 16 kDa protein has been isolated in a homogeneous form asthe major component of a paracrystalline paired membrane structureclosely resembling the gap junction. The primary structure ofthis protein from arthropod and vertebrate species has beendetermined by protein and cDNA sequencing. The amino acid sequencesare highly conserved and virtually identical to the amino acidsequence of the proteolipid subunit of the vacuolar H⁺-ATPases.The disposition of the protein in the membrane has been studiedusing proteases and the N,N'-dicyclohexylcarbodiimide reactivesite identified. These data, together with secondary structurepredictions, suggest that the 16 kDa protein is for the mostpart buried in the membrane, arranged in a bundle of four hydrophobicß-helices. Using computer graphics, a model has beenconstructed based on this arrangement and on the electron microscopicimages of the paracrystalline arrays