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Title
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Three-dimensional structure of beta-galactosidase from E. coli.
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Authors
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R.H.Jacobson,
X.J.Zhang,
R.F.DuBose,
B.W.Matthews.
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Ref.
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Nature, 1994,
369,
761-766.
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PubMed id
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Abstract
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The beta-galactosidase from Escherichia coli was instrumental in the development
of the operon model, and today is one of the most commonly used enzymes in
molecular biology. Here we report the structure of this protein and show that it
is a tetramer with 222-point symmetry. The 1,023-amino-acid polypeptide chain
folds into five sequential domains, with an extended segment at the amino
terminus. The participation of this amino-terminal segment in a subunit
interface, coupled with the observation that each active site is made up of
elements from two different subunits, provides a structural rationale for the
phenomenon of alpha-complementation. The structure represents the longest
polypeptide chain for which an atomic structure has been determined. Our results
show that it is possible successfully to study non-viral protein crystals with
unit cell dimensions in excess of 500 A and with relative molecular masses in
the region of 2,000K per asymmetric unit. Non-crystallographic symmetry
averaging proved to be a very powerful tool in the structure determination, as
has been shown in other contexts.
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