Structure of the Rotor of the V-Type Na + -ATPase from Enterococcus hirae

Abstract

The membrane rotor ring from the vacuolar-type (V-type) sodium ion–pumping adenosine triphosphatase (Na ⁺ -ATPase) from Enterococcus hirae consists of 10 NtpK subunits, which are homologs of the 16-kilodalton and 8-kilodalton proteolipids found in other V-ATPases and in F ₁ F _o - or F-ATPases, respectively. Each NtpK subunit has four transmembrane α helices, with a sodium ion bound between helices 2 and 4 at a site buried deeply in the membrane that includes the essential residue glutamate-139. This site is probably connected to the membrane surface by two half-channels in subunit NtpI, against which the ring rotates. Symmetry mismatch between the rotor and catalytic domains appears to be an intrinsic feature of both V- and F-ATPases.