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Title
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How amino-acid insertions are allowed in an alpha-helix of T4 lysozyme.
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Authors
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D.W.Heinz,
W.A.Baase,
F.W.Dahlquist,
B.W.Matthews.
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Ref.
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Nature, 1993,
361,
561-564.
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PubMed id
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Abstract
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Studies of extant protein sequences indicate that amino-acid insertions and
deletions are preferentially located in loop regions, which has traditionally
been explained as the result of selection removing deleterious mutations within
secondary structural elements from the population. But there is no a priori
reason to discount the possibility that insertions within secondary structure
could either be tolerated until compensatory mutations arise, or have effects
that are propagated away from secondary structure into loops. Earlier studies
have indicated that insertions are generally tolerated, although much less well
within secondary structure elements than in loop regions. Here we show that
amino-acid insertions in an alpha-helix of T4 lysozyme can be accepted in two
different ways. In some cases the inserted amino acids are accommodated within
the helix, leading to the translocation of wild-type residues from the helix to
the preceding loop. In other cases the insertion causes a 'looping-out' in the
first or last turn of the helix. The individual structural responses seem to be
dominated by the maintenance of the interface between the helix and the rest of
the protein.
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