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PDBsum entry 1ab6
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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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Structure analysis of two chey mutants: importance of the hydrogen-Bond contribution to protein stability.
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Authors
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D.Wilcock,
M.T.Pisabarro,
E.López-Hernandez,
L.Serrano,
M.Coll.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 1998,
54,
378-385.
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PubMed id
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Abstract
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The crystal structures of two double mutants (F14N/V21T and F14N/V86T) of the
signal transduction protein CheY have been determined to a resolution of 2.4 and
2.2 A, respectively. The structures were solved by molecular replacement and
refined to final R values of 18.4 and 19.2%, respectively. Together with
urea-denaturation experiments the structures have been used to analyse the
effects of mutations where hydrophobic residues are replaced by residues capable
of establishing hydrogen bonds. The large increase in stabilization (-12.1 kJ
mol-1) of the mutation Phe14Asn arises from two factors: a reverse hydrophobic
effect and the formation of a good N-cap at alpha-helix 1. In addition, a
forward-backward hydrogen-bonding pattern, resembling an N-capping box and
involving Asn14 and Arg18, has been found. The two Val to Thr mutations at the
hydrophobic core have different thermodynamic effects: the mutation Val21Thr
does not affect the stability of the protein while the mutation Val86Thr causes
a small destabilization of 1.7 kJ mol-1. At site 21 a backward side
chain-to-backbone hydrogen bond is formed inside alpha-helix 1 with the carbonyl
O atom of the i - 4 residue without movement of the mutated side chain. The
destabilizing effect of introducing a polar group in the core is efficiently
compensated for by the formation of an extra hydrogen bond. At site 86 the new
Ogamma atom escapes from the hydrophobic environment by a chi1 rotation into an
adjacent hydrophilic cavity to form a new hydrogen bond. In this case the
isosteric Val to Thr substitution is disruptive but the loss in stabilization
energy is partly compensated by the formation of a hydrogen bond. The two
crystal structures described in this work underline the significance of the
hydrogen-bond component to protein stability.
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