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Title
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Conformation, protein-carbohydrate interactions and a novel subunit association in the refined structure of peanut lectin-lactose complex.
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Authors
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R.Banerjee,
K.Das,
R.Ravishankar,
K.Suguna,
A.Surolia,
M.Vijayan.
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Ref.
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J Mol Biol, 1996,
259,
281-296.
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PubMed id
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Abstract
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The structure of the complex of the tetrameric peanut lectin with lactose has
been refined to an R-value of 16.4% using 2.25 angstroms resolution X-ray
diffraction data. The subunit conformation in the structure is similar to that
in other legume lectins except in the loops. It has been shown that in the
tertiary structure of legume lectins, the short five-stranded sheet plays a
major role in connecting the larger flat six-stranded and curved seven-stranded
sheets. Furthermore, the loops that connect the strands at the two ends of the
seven-stranded sheet curve toward and interact with each other to produce a
second hydrophobic core in addition to the one between the two large sheets. The
protein-lactose interactions involve the invariant features observed in other
legume lectins in addition to those characteristic of peanut lectin. The "open"
quaternary association in peanut lectin is stabilised by hydrophobic,
hydrogen-bonded and water-mediated interactions. Contrary to the earlier belief,
the structure of peanut lectin demonstrates that the variability in quaternary
association in legume lectins, despite all of them having nearly the same
tertiary structure, is not necessarily caused by covalently bound carbohydrate.
An attempt has been made to provide a structural rationale for this variability,
on the basis of buried surface areas during dimerisation. A total of 45 water
molecules remain invariant when the hydration shells of the four subunits are
compared. A majority of them appear to be involved in stabilising loops.
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