7 research outputs found
Amino acid sequence and disulphide-bridge pattern of three g-thionins from Sorghum bicolor
The complete primary structure of a new a-amylase inhibitor from Sorghum bicolor belonging to the
y-thionin family has been determined and the amino acid sequences of two components of the family
already elucidated have been corrected by combining the classical Edman degradation with advanced
mass spectrometric procedures. The same integrated approach allowed us to define the pattern of the
disulphide bridges in the three isoinhibitors. The arrangement of the cysteine pairing was determined as
Cys3-Cys47, Cys14-Cys34, Cys20-Cys41 and Cys24-Cys43.
The amino acid sequences of the a-amylase inhibitors share a high degree of similarity with the
related plant y-thionins. All these proteins consist of 47 residues, contain eight cysteine residues forming
four disulphide bridges, and show the presence of two clusters of basic amino acids located at both ends
of the polypeptide chain. The pattern of S-S bridges determined for the isoinhibitors is identical to that
inferred by NMR analysis in two related y-thionins, thus suggesting a highly conserved organization of
the disulphide pairing.
These results indicate that the structural similarities among the different y-thionins extend far beyond
the primary structure and possibly concern the secondary structure and the general folding of the entire
y-thionin family