E. coli F₁-ATPase interacts with a membrane protein component of a proton channel

Abstract

The ATP synthases of bacteria, mitochondria and chloroplasts, which use the energy of a transmembrane proton gradient to power the synthesis of ATP, consist of an integral membrane component F₀—thought to contain a proton channel—and a catalytic component, F₁. To help investigate the way F₀ and F₁ are coupled, we have sequenced the b-subunit of the Escherichia coli F₀, which seems to be the counterpart of a thermophilic bacteria F₀ summit thought to be essential for F₁ binding¹. We report here that its sequence is remarkable, being hydrophobic around the N-terminus and highly charged in the remainder. We propose that the N-terminal segment lies in the membrane and the rest outside. The extramembranous section contains two adjacent stretches of 31 amino acids where the sequence is very similar: in the second of these stretches there is further internal homology. These duplicated stretches of the polypeptide probably fold into two α-helices which have many common features able to make contact with F₁ subuits. Thus protein b occupies a central position in the enzyme, where it may be involved in proton translocation. It is possibly also important in biosynthetic assembly.