MoleCillat'lmprovement of Food Functional Properties of Soybean Glycinin by Protein Engineering

Abstract

A study was made to elucidate the three dimensional structure of soybean glydnin which is one of the dominant storage proteins of soybean seeds. Previously, the twodisulphide bonds Cys12-Cys45 and Cys88-Cys298 in the proglydnin AlaBlb subunit were deleted andCys residues were replaced by Gly and Ser by Oligonucleotide-directed mutagenesis. The mutant proglycinins Gly12, and Ser88 showed to have better gelation and emulsifying properties. The mutant proglydnins were crystallised along with the normal proglycinin (AlaBlb -3) and subjected to X-ray structure analysis in an attempt to determine their structure-junction relationships. The crystals diffracted X-ray to a resollttion limit of 2.9 - 3.4A on stillphotographs and belongto the tetragonal system, space group P41 or P43 with cell dimensions of a = b= 114.3 - 115.2A. and c= 145.7 - 147.1A with 3 protomers per asymmetric unit. Further refinement data for the' crystals of normal prpglycinin were obtained by multiple isomorphous replacement and solvent flattening techniques. The tri1?ler dimensions of tlie normal proglydnin as determined at 6A were 93A by 93A with·the thickness of 36A. .

Key words: Crystallisation, Proglycinin, Protein Engineering, Soybean gfycinin, X-ray Crystallography