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PDBsum entry 1xrd
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Membrane protein
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PDB id
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1xrd
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References listed in PDB file
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Key reference
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Title
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Solution structures of the core light-Harvesting alpha and beta polypeptides from rhodospirillum rubrum: implications for the pigment-Protein and protein-Protein interactions.
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Authors
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Z.Y.Wang,
K.Gokan,
M.Kobayashi,
T.Nozawa.
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Ref.
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J Mol Biol, 2005,
347,
465-477.
[DOI no: ]
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PubMed id
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Abstract
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We have determined the solution structures of the core light-harvesting (LH1)
alpha and beta-polypeptides from wild-type purple photosynthetic bacterium
Rhodospirillum rubrum using multidimensional NMR spectroscopy. The two
polypeptides form stable alpha helices in organic solution. The structure of
alpha-polypeptide consists of a long helix of 32 amino acid residues over the
central transmembrane domain and a short helical segment at the N terminus that
is followed by a three-residue loop. Pigment-coordinating histidine residue
(His29) in the alpha-polypeptide is located near the middle of the central
helix. The structure of beta-polypeptide shows a single helix of 32 amino acid
residues in the membrane-spanning region with the pigment-coordinating histidine
residue (His38) at a position close to the C-terminal end of the helix. Strong
hydrogen bonds have been identified for the backbone amide protons over the
central helical regions, indicating a rigid property of the two polypeptides.
The overall structures of the R.rubrum LH1 alpha and beta-polypeptides are
different from those previously reported for the LH1 beta-polypeptide of
Rhodobacter sphaeroides, but are very similar to the structures of the
corresponding LH2 alpha and beta-polypeptides determined by X-ray
crystallography. A model constructed for the structural subunit (B820) of LH1
complex using the solution structures reveals several important features on the
interactions between the LH1 alpha and beta-polypeptides. The significance of
the N-terminal regions of the two polypeptides for stabilizing both B820 and LH1
complexes, as clarified by many experiments, may be attributed to the
interactions between the short N-terminal helix (Trp2-Gln6) of alpha-polypeptide
and a GxxxG motif in the beta-polypeptide.
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Figure 7.
Figure 7. A model for the B820 subunit constructed
using the LH1 a and b structures of this study and BChl a
molecules. The structure of BChl a was adopted from the
crystal structure of LH2 complex (PDB entry 1LGH)
determined for Ps. molischianum. (a) Side view showing
the BChl a alignment in the transmembrane helical
domains and relative position of the N-terminal helix
and loop of the a-polypeptide to the helical region of the
b-polypeptide. (b) Top view of the structure in (a) from
the C terminus showing the partial overlap between the
two BChl a molecules colored in cyan.
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The above figure is
reprinted
by permission from Elsevier:
J Mol Biol
(2005,
347,
465-477)
copyright 2005.
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