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PDBsum entry 1k3m
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Hormone/growth factor
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PDB id
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1k3m
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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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A cavity-Forming mutation in insulin induces segmental unfolding of a surrounding alpha-Helix.
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Authors
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B.Xu,
Q.X.Hua,
S.H.Nakagawa,
W.Jia,
Y.C.Chu,
P.G.Katsoyannis,
M.A.Weiss.
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Ref.
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Protein Sci, 2002,
11,
104-116.
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PubMed id
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Abstract
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To investigate the cooperativity of insulin's structure, a cavity-forming
substitution was introduced within the hydrophobic core of an engineered
monomer. The substitution, Ile(A2)-->Ala in the A1-A8 alpha-helix, does not
impair disulfide pairing between chains. In accord with past studies of
cavity-forming mutations in globular proteins, a decrement was observed in
thermodynamic stability (DeltaDeltaG(u) 0.4-1.2 kcal/mole). Unexpectedly, CD
studies indicate an attenuated alpha-helix content, which is assigned by NMR
spectroscopy to selective destabilization of the A1-A8 segment. The analog's
solution structure is otherwise similar to that of native insulin, including the
B chain's supersecondary structure and a major portion of the hydrophobic core.
Our results show that (1) a cavity-forming mutation in a globular protein can
lead to segmental unfolding, (2) tertiary packing of Ile(A2), a residue of low
helical propensity, stabilizes the A1-A8 alpha-helix, and (3) folding of this
segment is not required for native disulfide pairing or overall structure. We
discuss these results in relation to a hierarchical pathway of protein folding
and misfolding. The Ala(A2) analog's low biological activity (0.5% relative to
the parent monomer) highlights the importance of the A1-A8 alpha-helix in
receptor recognition.
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