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PDBsum entry 1pwt
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Circular permutant
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PDB id
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1pwt
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References listed in PDB file
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Key reference
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Title
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Thermodynamic analysis of alpha-Spectrin sh3 and two of its circular permutants with different loop lengths: discerning the reasons for rapid folding in proteins.
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Authors
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J.C.Martínez,
A.R.Viguera,
R.Berisio,
M.Wilmanns,
P.L.Mateo,
V.V.Filimonov,
L.Serrano.
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Ref.
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Biochemistry, 1999,
38,
549-559.
[DOI no: ]
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PubMed id
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Abstract
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The temperature dependences of the unfolding-refolding reaction of a shorter
version of the alpha-spectrin SH3 domain (PWT) used as a reference and of two
circular permutants (with different poly-Gly loop lengths at the newly created
fused loop) have been measured by differential scanning microcalorimetry and
stopped-flow kinetics, to characterize the thermodynamic nature of the
transition and native states. Differential scanning calorimetry results show
that all these species do not belong to the same temperature dependency of heat
effect. The family of the N47-D48s circular permutant (with 0-6 Gly inserted at
the fused-loop) shows a higher enthalpy as happens with the PWT domain. The wild
type (WT) and the S19-P20s permutant family have a more similar behavior
although the second is far less stable. The crystallographic structure of the
PWT shows a hairpin formation in the region corresponding to the unstructured
N-terminus tail of the WT, explaining the enthalpic difference. There is a very
good correlation between the calorimetric changes and the structural differences
between the WT, PWT, and two circular permutants that suggests that their
unfolded state cannot be too different. Elongation of the fused loop in the two
permutants, taking as a reference the protein with one inserted Gly, results in
a small Gibbs energy change of entropic origin as theoretically expected. Eyring
plots of the unfolding and refolding semireactions show different behaviors for
PWT, S19-P20s, and N47-D48s in agreement with previous studies indicating that
they have different transition states. The SH3 transition state is relatively
close to the native state with regard to changes in heat capacity and entropy,
indicating a high degree of compactness and order. Regarding the differences in
thermodynamic parameters, it seems that rapid folding could be achieved in
proteins by decreasing the entropic barrier.
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