Ion binding and selectivity of the rotor ring of the Na+-transporting V-ATPase.
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.
Murata
Takeshi
T
Department of Cell Biology, Faculty of Medicine, Kyoto University, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan. t.murata@mfour.med.kyoto-u.ac.jp
Yamato
Ichiro
I
Kakinuma
Yoshimi
Y
Shirouzu
Mikako
M
Walker
John E
JE
Yokoyama
Shigeyuki
S
Iwata
So
S
D001665:Binding Sites; D001692:Biological Transport; D002412:Cations / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D016983:Enterococcus / Q000201:enzymology; D007700:Kinetics; D008094:Lithium / Q000378:metabolism; D008954:Models, Biological; D008958:Models, Molecular; D012964:Sodium / Q000378:metabolism*; D025262:Vacuolar Proton-Translocating ATPases / Q000737:chemistry* / Q000378:metabolism*
D002412:Cations; D008094:Lithium; D012964:Sodium; D025262:Vacuolar Proton-Translocating ATPases