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 F1Fo- or F-ATPases, respectively. Each NtpK subunit has four transmembrane alpha 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.

A conserved residue, PomB-F22, in the transmembrane segment of the flagellar stator complex, has a critical role in conducting ions and generating torque

“…We think that PomA-N194 might be one of the most important residues for ion specificity, although there are probably other residues that contribute. NtpK, which is a V-ATPase rotor ring component, coordinates Na + with the essential carboxyl group of E139, the carbonyl group of Q65 and Q110, the hydroxyl group of T64 and the main chain carbonyl group of L61 (Murata et al, 2005).…”

“…For example, in the Na + -driven V-type ATPase of Enterococcus hirae, the transmembrane complex V o , which conducts Na + (or Li + ), is composed of a membrane rotor ring (K-ring) comprising oligomers of NtpK and a single copy of the NtpI subunit. It has been suggested that the cavity size of the K-ring binding pocket contributes to the ion specificity, that five residues (L 61 , T 64 , Q 65 , Q 110 , E 139 ) of NtpK are involved in the Na + binding to the K-ring, and that the essential glutamate E 139 is conserved in the homologous subunits of H + -driven VATPase (Murata et al, 2005(Murata et al, , 2008. Bacterial flagellar motors are rotary motors which convert the electrochemical potential difference of a coupling ion (H + or Na + ) across the cytoplasmic membrane into torque, which rotates the flagellum.…”

“…Each selective ion transporter, which is coupled to a sodium ion, such as LeuT, NtpK or NhaA, possesses an ion binding pocket. A particular ion and/or a transport substrate interacts with the ion binding pocket, induces a conformational change, and is then translocated to the opposite side across the membrane (Gouaux & Mackinnon, 2005;Yamashita et al, 2005;Hunte et al, 2005;Murata et al, 2005Murata et al, , 2008. For example, in the Na + -driven V-type ATPase of Enterococcus hirae, the transmembrane complex V o , which conducts Na + (or Li + ), is composed of a membrane rotor ring (K-ring) comprising oligomers of NtpK and a single copy of the NtpI subunit.…”

The First Hydroxylated Archazolid from the Myxobacterium Cystobacter violaceus: Isolation, Structural Elucidation and V-ATPase Inhibition

“…This subunit forms an oligomer, building up a ring structure of six or more copies which transports protons across the membrane. Recently, the structure of the ring from a bacterial V-ATPase has been described at 2.1 Å resolution and showed that 10 copies form the c ring [4]. This increasing molecular understanding in combination with the very promising biological profile of the archazolids renders these macrolide antibiotics attractive structures for further development.…”

Significance of the Glutamate-139 Residue of the V-Type Na+-ATPase NtpK Subunit in Catalytic Turnover Linked with Salt Tolerance of Enterococcus hirae

“…E. hirae V-ATPase requires all of its nine subunits (NtpFIKECGABD) (15) for its activity (5). The NtpK subunit forms the rotor ring of the V o moiety, which is responsible for ion translocation (17), and the Glu139 residue of NtpK, which constitutes the ion binding site (18), is crucial for its catalytic mechanism (21). Notably, E. hirae V-ATPase recognizes Na ϩ and Li ϩ with nearly equal affinities.…”