Ion binding and selectivity of the rotor ring of the Na+-transporting V-ATPase.

TitleIon binding and selectivity of the rotor ring of the Na+-transporting V-ATPase.
Publication TypeJournal Article
Year of Publication2008
AuthorsMurata, T, Yamato, I, Kakinuma, Y, Shirouzu, M, Walker, JE, Yokoyama, S, Iwata, S
JournalProc Natl Acad Sci U S A
Volume105
Issue25
Pagination8607-12
Date Published2008 Jun 24
ISSN1091-6490
KeywordsBinding Sites, Biological Transport, Cations, Crystallography, X-Ray, Enterococcus, Kinetics, Lithium, Models, Biological, Models, Molecular, Sodium, Vacuolar Proton-Translocating ATPases
Abstract

The vacuole-type ATPases (V-ATPases) are proton pumps in various intracellular compartments of eukaryotic cells. Prokaryotic V-ATPase of Enterococcus hirae, closely related to the eukaryotic enzymes, provides a unique opportunity to study ion translocation by V-ATPases because it transports Na(+) ions, which are easier to detect by x-ray crystallography and radioisotope experiments. The purified rotor ring (K-ring) of the E. hirae V-ATPase binds one Na(+) ion per K-monomer with high affinity, which is competitively inhibited by Li(+) or H(+), suggesting that the K-ring can also bind these ions. This finding is also supported by the K-ring structure at 2.8 A in the presence of Li(+). Association and dissociation rates of the Na(+) to and from the purified K-ring were extremely slow compared with the Na(+) translocation rate estimated from the enzymatic activity, strongly suggesting that interaction with the stator subunit (I-subunit) is essential for Na(+) binding to /release from the K-ring.

DOI10.1073/pnas.0800992105
Alternate JournalProc. Natl. Acad. Sci. U.S.A.
Citation Key10.1073/pnas.0800992105
PubMed ID18559856
PubMed Central IDPMC2438407
Grant ListMC_U105663150 / / Medical Research Council / United Kingdom