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Title
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The secondary structure of echistatin from 1H-NMR, circular-dichroism and Raman spectroscopy.
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Authors
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V.Saudek,
R.A.Atkinson,
P.Lepage,
J.T.Pelton.
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Ref.
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Eur J Biochem, 1991,
202,
329-338.
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PubMed id
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Abstract
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Detailed biophysical studies have been carried out on echistatin, a member of
the disintegrin family of small, cysteine-rich, RGD-containing proteins,
isolated from the venom of the saw-scaled viper Echis carinatus. Analysis of
circular-dichroism spectra indicates that, at 20 degrees C, echistatin contains
no alpha-helix but contains mostly beta-turns and beta-sheet. Two isobestic
points are observed as the temperature is raised, the conformational changes
associated with that observed between 40 degrees C and 72 degrees C being
irreversible. Raman spectra also indicate considerable beta-turn and beta-sheet
(20%) structure and an absence of alpha-helical structure. Three of the four
disulphide bridges are shown to be in an all-gauche conformation, while the
fourth adopts a trans-gauche-gauche conformation. The 1H-NMR spectrum of
echistatin has been almost fully assigned. A single conformation was observed at
27 degrees C with the four proline residues adopting only the trans
conformation. A large number of backbone amide protons were found to exchange
slowly, but no segments of the backbone were found to be in either alpha-helical
or beta-sheet conformation. A number of turns could be characterised. An
irregular beta-hairpin contains the RGD sequence in a mobile loop at its tip.
Two of the four disulphide cross-links have been identified from the NMR
spectra. The data presented in this paper will serve to define the structure of
echistatin more closely in subsequent studies.
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