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Title
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Structure of ricin A-chain at 2.5 A.
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Authors
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B.J.Katzin,
E.J.Collins,
J.D.Robertus.
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Ref.
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Proteins, 1991,
10,
251-259.
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PubMed id
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Abstract
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Ricin has been refined in a crystallographic sense to 2.5 A resolution and the
model for the A-chain (RTA) is described in detail. Because RTA is the first
member of the class of plant toxins to be analyzed, this model probably defines
the major structural characteristics of the entire family of these medically
important proteins. Explanations are provided to rationalize amino acids that
are conserved between RTA and a number of homologous plant and bacterial toxins.
Eight invariant residues appear to be involved in creating or stabilizing the
active site. In the active site Arg180 and Glu177 are hydrogen bonded to each
other and also coordinate a water molecule; each of these groups may be
important in the N-glycosidation reaction. Several other polar residues may play
lesser roles in the mechanism, including tyrosines 80 and 123 and asparagines 78
and 209. A number of conserved hydrophobic residues are seen to cluster within
several patches and probably drive the overall folding of the toxin molecule.
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