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Title
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1.67-A X-ray structure of the B2 immunoglobulin-binding domain of streptococcal protein G and comparison to the NMR structure of the B1 domain.
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Authors
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A.Achari,
S.P.Hale,
A.J.Howard,
G.M.Clore,
A.M.Gronenborn,
K.D.Hardman,
M.Whitlow.
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Ref.
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Biochemistry, 1992,
31,
10449-10457.
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PubMed id
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Abstract
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The structure of the B2 immunoglobulin-binding domain of streptococcal protein G
has been determined at 1.67-A resolution using a combination of single
isomorphous replacement (SIR) phasing and manual fitting of the coordinates of
the NMR structure of B1 domain of streptococcal protein G [Gronenborn, A. M., et
al. (1991) Science 253, 657-661]. The final R value was 0.191 for data between
8.0 and 1.67 A. The structure described here has 13 residues preceding the
57-residue Ig-binding domain and 13 additional residues following it, for a
total of 83 residues. The 57-residue binding domain is well-determined in the
structure, having an average B factor of 18.0. Only residues 8-77 could be
located in the electron density maps, with the ends of the structure fading into
disorder. Like the B1 domain, the B2 domain consists of four beta-strands and a
single helix lying diagonally across the beta-sheet, with a -1, +3 chi, -1
topology. This small structure is extensively hydrogen-bonded and has a
relatively large hydrophobic core. These structural observations may account for
the exceptional stability of protein G. A comparison of the B2 domain X-ray
structure and the B1 domain NMR structure showed minor differences in the turn
between strands and two and a slight displacement of the helix relative to the
sheet. Hydrogen bonds between crystallographically related molecules account for
most of these differences.
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