STRUCTURE AND FUNCTION OF RELATED PROTON CHANNEL-FORMING PROTEINS

A molecular model has been constructed for a 16 kDa integral membrane protein which is the principal component of gap junction-like structures in the arthropod Nephrops norvegicus. This proteolipid is a member of a family of highly conserved proteins comprising the proton channel-forming subunits of vacuolar membrane (V-type) ATPases. The model suggests that the polypeptide exists as a transmembrane four-helical bundle, which assembles as a hexamer to form the membrane-spanning channel. The arthropod protein has been cloned and subsequently expressed in yeast, in which it complements a mutation in the endogenous gene for the related vacuolar membrane ATPase channel-forming subunit. Mutagenesis studies have been initiated in the yeast system in order to validate the structural model and to examine ion selectivity and transport mechanisms.