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Title
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The effect of a proline residue on the rate of growth and the space group of alpha-spectrin SH3-domain crystals.
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Authors
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A.Cámara-Artigas,
M.Andújar-Sánchez,
E.Ortiz-Salmerón,
C.Cuadri,
S.Casares.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 2009,
65,
1247-1252.
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PubMed id
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Abstract
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alpha-Spectrin SH3-domain (Spc-SH3) crystallization is characterized by very
fast growth of the crystals in the presence of ammonium sulfate as a precipitant
agent. The origin of this behaviour can be attributed to the presence of a
proline residue that participates in a crystal contact mimicking the binding of
proline-rich sequences to SH3 domains. This residue, Pro20, is located in the RT
loop and is the main contact in one of the interfaces present in the
orthorhombic Spc-SH3 crystal structures. In order to understand the molecular
interactions that are responsible for the very fast crystal growth of the
wild-type (WT) Spc-SH3 crystals, the crystal structure of a triple mutant in
which the residues Ser19-Pro20-Arg21 in the RT loop have been replaced by
Gly19-Asp20-Ser21 (GDS Spc-SH3 mutant) has been solved. The removal of the
critical proline residue results in slower nucleation of the Spc-SH3 crystals
and a different arrangement of the protein molecules in the unit cell, leading
to a crystal that belongs to the tetragonal space group P4(1)2(1)2, with
unit-cell parameters a = b = 42.231, c = 93.655 A, and that diffracts to 1.45 A
resolution. For both WT Spc-SH3 and the GDS mutant, light-scattering experiments
showed that a dimer was formed in solution within a few minutes of the addition
of 2 M ammonium sulfate at pH 6.5 and allowed the proposal of a mechanism for
the nucleation and crystal growth of Spc-SH3 in which the Pro20 residue plays a
key role in the rate of crystal growth.
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