A molecular model has been constructed for a 16 kDa integral membrane
protein which is the principal component of gap junction-like structur
es 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 sug
gests that the polypeptide exists as a transmembrane four-helical bund
le, 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 t
he related vacuolar membrane ATPase channel-forming subunit. Mutagenes
is studies have been initiated in the yeast system in order to validat
e the structural model and to examine ion selectivity and transport me
chanisms.