Family 3.A.2 - The H+ or Na+ translocating F-type, V-type and
A-type ATPase Superfamily
Family ID: 52650
F-type ATPases are found in eukaryotic mitochondria and chloroplasts
as well as in bacteria. V-type ATPases are found in vacuoles of
eukaryotes and in bacteria. A-type ATPases are found in archaea.
All such systems are multisubunit complexes with at least 3 dissimilar
subunits embedded as a complex in the membrane (F0, a:b:c = 1:2:~12)
and (usually) at least 5 dissimilar subunits attached to F0 (F1,
a:b:g:d:e = 3:3:1:1:1 for F-type ATPases). The eukaryotic proteins
are more complicated than the bacterial enzyme complexes. The
a, b, d and F1 hexamer (a3b3) comprise the stator which is believed
to rotate relative to the rotor (which consists of the c, e and
g subunits) in response to either ATP hydrolysis by F1 or proton
transport through F0. H+ transport and ATP synthesis may therefore
be coupled mechanically. The F1 portion of the bovine mitochondrial
F-type ATPase has been solved to 2.8 Å resolution.
All eukaryotic
F-type ATPases pump 3-4 H+ out of mitochondria, or into thylakoids
of chloroplasts, per ATP hydrolyzed. Bacterial F-type ATPases
pump 3-4 H+ and/or Na+ (depending on the system) out of the cell
per ATP hydrolyzed. These enzymes also operate in the opposite
direction, synthesizing ATP when protons flow through the "ATP
synthase" down the proton electrochemical gradient (the "proton
motive force" or pmf). V-type ATPases may pump 2-3 H+ per
ATP hydrolyzed.
Phylogenetic
clustering of the integral membrane constituents of F-type ATPases
generally corresponds to the phylogenies of the organisms of origin,
and consequently the systems in different organisms are probably
orthologues. The a subunit of F0 (one copy per complex) spans
the membrane five or six times. The b subunits (2 copies per complex;
heterodimeric in plant chloroplasts and blue green bacteria) span
the membrane once; and the c subunits (called DCCD-binding lipoproteins;
12 copies per complex) span the membrane two times. Some F-type
ATPases such as the Na+-translocating ATPase of Acetobacterium
woodii probably contains 3 dissimilar but homologous c-subunit
proteolipids of 8 and 18 kDa. The V-type ATPase of S. cerevisiae
also has 3 dissimilar c-subunits as mentioned in the next paragraph.
The a, b and
c-subunits of F-type ATPases are homologues to the B, A and c-
(or K-) subunits of V-type and A-type ATPases, respectively. Other
subunits in these protein complexes are probably homologous to
each other, but this fact can not always be demonstrated by statistical
analyses of the sequencs. Thus, for the A-type ATPase of Methanosarcina
mazei, theV-type ATPase of yeast, and the F-type ATPase of E.
coli, respectively, the following subunit equivalences have been
suggested: A = Vma1 (A) = b; B = Vma2 (B) = a; C = Vma6 (d) =
no E. coli F-type ATPase equivalent; Vma8 (D) = g; Vma4 (E) =
d; F = Vma7 (F) = e; I = Vphl/stvl = a+b ?, and K = Vma3 (c) =
c. Additionally, the yeast v-type ATPase has 3 dissimilar c-subunits:
Vma3(c), Vmal1(c) and Vma6(c), and three subunits, Vma13(H), Vma5(c)
and Vma10(G) which are not found in either the A- or F-type ATPases.
All of the yeast vacurlar ATPase subunits have an equivalent subunit
in the V-type ATPases of clathrin-coated vesicles of higher eukaryotes.
