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Title
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Functional inferences from crystals of Escherichia coli trp repressor.
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Authors
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A.Joachimiak,
R.W.Schevitz,
R.L.Kelley,
C.Yanofsky,
P.B.Sigler.
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Ref.
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J Biol Chem, 1983,
258,
12641-12643.
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PubMed id
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Abstract
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We have reproducibly grown crystals of L-tryptophan . trp aporepressor and
indole-3-propionate . trp aporepressor complexes from Escherichia coli which are
suitable for x-ray diffraction analysis. The active repressor, L-tryptophan .
aporepressor, crystallizes in both trigonal (P3(1)21 or P3(2)21) and tetragonal
(P4(1)22 or P4(3)22) forms which diffract to at least 2.0 and 2.5 A,
respectively. The trigonal form has one-half of the functional dimer/asymmetric
unit; therefore, the trp repressor molecule has an axis of 2-fold rotational
symmetry corresponding to the lattice dyad. The inactive complex,
indole-3-propionate . aporepressor, or "pseudorepressor," forms tetragonal
crystals that also diffract to at least 2.5 A and are isomorphous to those of
the active repressor. Slight differences between their diffraction patterns
indicate modest structural differences between active and inactive complexes
that are presumably mediated by the alpha-amino group of L-tryptophan and
account for operator-specific binding.
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