Accelerated Publications
Solution Structure of the Transmembrane H
+
-Transporting Subunit c of the F
1
F
o
ATP Synthase
†
Mark E. Girvin,*
,‡,§
Vinit K. Rastogi,
§
Frits Abildgaard,
|
John L. Markley,
|
and Robert H. Fillingame*
,‡
Department of Biomolecular Chemistry, UniVersity of Wisconsin Medical School, and Biochemistry Department, UniVersity of
Wisconsin, Madison, Wisconsin 53706, and Biochemistry Department, Albert Einstein College of Medicine,
1300 Morris Park AVenue, Bronx, New York 10461
ReceiVed March 4, 1998; ReVised Manuscript ReceiVed April 22, 1998
ABSTRACT: Subunit c is the H
+
-translocating component of the F
1
F
o
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
3
J
NR
, 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 F
o
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.
The F
1
F
o
ATP synthase uses a transmembrane electro-
chemical H
+
gradient to drive the synthesis of ATP from
ADP and P
i
. H
+
translocation through the membrane-
spanning F
o
portion of the enzyme drives ATP formation at
catalytic sites distantly located in the extrinsic, F
1
sector of
the enzyme. The crystal structure of the R
3
3
γ portion of
F
1
shows three R and three subunits alternating at the
†
This study was supported by U.S. Public Health Service Grants
GM23105 (R.H.F.) and GM55371 (M.E.G.). The National Magnetic
Resonance Facility at Madison, supported by NIH Grant R02301, was
used in this study. Equipment in the facility was purchased with funds
from the University of Wisconsin, the NSF Biological Instrumentation
Program (Grant DMB8415048), the NIH Biomedical Research Tech-
nology Program (RR02301), the NIH Shared Instrumentation Program
(Grant RR02781), and the U.S. Department of Agriculture. The
AECOM Structural NMR Resource, supported by Albert Einstein
College of Medicine and the NSF Academic Research Infrastructure
Program (DBI9601607), was also used in this study.
* Authors to whom correspondence should be addressed. M.E.G.:
telephone, (718) 430-2025; fax, (718) 430-8565; e-mail, girvin@
aecom.yu.edu. R.H.F.: telephone, (608) 262-1439; fax, (608) 262-5253;
e-mail, filingam@macc.wisc.edu.
‡
University of Wisconsin Medical School.
§
Albert Einstein College of Medicine.
|
University of Wisconsin.
© Copyright 1998 by the American Chemical Society Volume 37, Number 25 June 23, 1998
S0006-2960(98)00511-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 06/05/1998