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PDBsum entry 1f4z
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Proton transport, membrane protein
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PDB id
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1f4z
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Coupling photoisomerization of retinal to directional transport in bacteriorhodopsin.
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Authors
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H.Luecke,
B.Schobert,
J.P.Cartailler,
H.T.Richter,
A.Rosengarth,
R.Needleman,
J.K.Lanyi.
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Ref.
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J Mol Biol, 2000,
300,
1237-1255.
[DOI no: ]
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PubMed id
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Abstract
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In order to understand how isomerization of the retinal drives unidirectional
transmembrane ion transport in bacteriorhodopsin, we determined the atomic
structures of the BR state and M photointermediate of the E204Q mutant, to 1.7
and 1.8 A resolution, respectively. Comparison of this M, in which proton
release to the extracellular surface is blocked, with the previously determined
M in the D96N mutant indicates that the changes in the extracellular region are
initiated by changes in the electrostatic interactions of the retinal Schiff
base with Asp85 and Asp212, but those on the cytoplasmic side originate from
steric conflict of the 13-methyl retinal group with Trp182 and distortion of the
pi-bulge of helix G. The structural changes suggest that protonation of Asp85
initiates a cascade of atomic displacements in the extracellular region that
cause release of a proton to the surface. The progressive relaxation of the
strained 13-cis retinal chain with deprotonated Schiff base, in turn, initiates
atomic displacements in the cytoplasmic region that cause the intercalation of a
hydrogen-bonded water molecule between Thr46 and Asp96. This accounts for the
lowering of the pK(a) of Asp96, which then reprotonates the Schiff base via a
newly formed chain of water molecules that is extending toward the Schiff base.
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Figure 2.
Figure 2. 2F[o] -F[c] density maps of BR and M states of
E204Q, contoured at 1s, of the region of the retinal, Lys216,
Asp85, Trp182, and water molecules 401, 402, 501, 502, and 503.
(a) BR state; (b) M state.
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Figure 7.
Figure 7. Models of BR, earlier M (from E204Q) and late M
(from D96N) of the region that includes the retinal, Trp182,
Thr178, Lys216, Ala215, Thr46, Asp96, and water molecules 501,
502, 503 and 504, shown in stereo view. Color code for the BR,
and the earlier and late M states, as in Figure 3. (a)
Comparison of the BR and M states of the E204Q mutant. (b)
Comparison of the BR and M states of the D96N mutant.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2000,
300,
1237-1255)
copyright 2000.
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