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Title
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1H NMR assignment and global fold of napin BnIb, a representative 2S albumin seed protein.
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Authors
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M.Rico,
M.Bruix,
C.González,
R.I.Monsalve,
R.Rodríguez.
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Ref.
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Biochemistry, 1996,
35,
15672-15682.
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PubMed id
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Abstract
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Napin BnIb is a representative member of the 2S albumin seed proteins, which
consists of two polypeptide chains of 3.8 and 8.4 kDa linked by two disulfide
bridges. In this work, a complete assignment of the 1H spectra of napin BnIb has
been carried out by two-dimensional NMR sequence-specific methods and its
secondary structure determined on the basis of spectral data. A calculation of
the tertiary structure has been performed using approximately 500 distance
constraints derived from unambiguously assigned NOE cross-correlations and
distance geometry methods. The resulting global fold consists of five helices
and a C-terminal loop arranged in a right-handed spiral. The folded protein is
stabilized by two interchain disulfide bridges and two additional ones between
cysteine residues in the large chain. The structure of napin BnIb represents a
third example of a new and distinctive folding pattern first described for the
hydrophobic protein from soybean and nonspecific lipid transfer proteins from
wheat and maize. The presence of an internal cavity is not at all evident, which
rules out in principle the napin BnIb as a carrier of lipids. The determined
structure is compatible with activities attributed to these proteins such as
phospholipid vesicle interaction, allergenicity, and calmodulin antagonism.
Given the sequence homology of BnIb with other napins and napin-type 2S albumin
seed proteins from different species, it is likely that all these proteins share
a common architecture. The determined structure will be crucial to establish
structure-function relationships and to explore the mechanisms of folding,
processing, and deposition of these proteins. It will also provide a firm basis
for a rational use of genetic engineering in order to develop improved
transgenic plants.
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