bi980511m_si_001.pdf (200.91 kB)
Solution Structure of the Transmembrane H+-Transporting Subunit c of the F1Fo ATP Synthase†
journal contribution
posted on 1998-06-05, 00:00 authored by Mark E. Girvin, Vinit K. Rastogi, Frits Abildgaard, John L. Markley, Robert H. FillingameSubunit c is the H+-translocating component of the
F1Fo ATP synthase complex.
H+ transport
is coupled to conformational changes that ultimately lead to ATP
synthesis by the enzyme. The properties
of the monomeric subunit in a single-phase solution of
chloroform−methanol−water (4:4:1) have been
shown to mimic those of the protein in the native complex. Triple
resonance NMR experiments were
used to determine the complete structure of monomeric subunit c in this
solvent mixture. The structure
of the protein was defined by >2000 interproton distances, 64
3JNα, and 43
hydrogen-bonding NMR-derived restraints. The root mean squared deviation for the
backbone atoms of the two transmembrane
helices was 0.63 Å. The protein folds as a hairpin of two
antiparallel helical segments, connected by a
short structured loop. The conserved Arg41-Gln42-Pro43 form the
top of this loop. The essential H+-transporting Asp61 residue is located at a slight break in the middle of
the C-terminal helix, just prior to
Pro64. The C-terminal helix changes direction by 30 ± 5° at
the conserved Pro64. In its protonated
form, the Asp61 lies in a cavity created by the absence of side chains
at Gly23 and Gly27 in the N-terminal
helix. The shape and charge distribution of the molecular surface
of the monomeric protein suggest a
packing arrangement for the oligomeric protein in the Fo
complex, with the front face of one monomer
packing favorably against the back face of a second monomer. The
packing suggests that the proton
(cation) binding site lies between packed pairs of adjacent subunit
c.