The membrane domain of the Na+-motive V-ATPase from Enterococcus hirae contains a heptameric rotor.
In F-ATPases, ATP hydrolysis is coupled to translocation of ions through membranes by rotation of a ring of c subunits in the membrane. The ring is attached to a central shaft that penetrates the catalytic domain, which has pseudo-3-fold symmetry. The ion translocation pathway lies between the external circumference of the ring and another hydrophobic protein. The H+ or Na+:ATP ratio depends upon the number of ring protomers, each of which has an essential carboxylate involved directly in ion translocation. This number and the ratio differ according to the source, and 10, 11, and 14 protomers have been found in various enzymes, with corresponding calculated H+ or Na+:ATP ratios of 3.3, 3.7, and 4.7. V-ATPases are related in structure and function to F-ATPases. Oligomers of subunit K from the Na+-motive V-ATPase of Enterococcus hirae also form membrane rings but, as reported here, with 7-fold symmetry. Each protomer has one essential carboxylate. Thus, hydrolysis of one ATP provides energy to extrude 2.3 sodium ions. Symmetry mismatch between the catalytic and membrane domains appears to be an intrinsic feature of both V- and F-ATPases.
Murata
Takeshi
T
Medical Research Council Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, United Kingdom.
Arechaga
Ignacio
I
Fearnley
Ian M
IM
Kakinuma
Yoshimi
Y
Yamato
Ichiro
I
Walker
John E
JE
D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000201:enzymology; D016983:Enterococcus / Q000201:enzymology*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012964:Sodium / Q000378:metabolism*; D025262:Vacuolar Proton-Translocating ATPases / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure
D012964:Sodium; D025262:Vacuolar Proton-Translocating ATPases