THE PLANT CELL, Vol 2, Issue 5 403-413, Copyright © 1990 by American Society of Plant Biologists
Effect of Structural Modifications on the Assembly of a Glycinin Subunit
C. D. Dickinson, M. P. Scott, EHA. Hussein, P. Argos and N. C. Nielsen
United States Department of Agriculture, Agricultural Research Service and Agronomy Department, Purdue University, West Lafayette, Indiana 47907
A Gy4 glycinin cDNA was modified and used to produce structurally altered
11S storage protein subunits. We evaluated these modified subunits for
their ability to assemble into oligomers. Alterations made in the acidic
polypeptide changed the subunit solubility characteristics but did not
eliminate assembly. Modifications in the basic polypeptide usually
eliminated assembly of subunits into trimers. A region exhibiting high
natural variability located at the COOH terminus of the acidic polypeptide
that we have designated the hypervariable region was also studied.
Extensive deletions and insertions were tolerated in the hypervariable
region without perturbing subunit assembly. Some of the insertions
significantly increased the methionine content in the Gy4 glycinin subunit.
Together, our results indicated that the structure of the basic polypeptide
was more critical for assembly of trimers than that of the acidic
polypeptide, an observation that implies that the basic polypeptides direct
trimer formation. The assembly assays described here will be useful in
efforts to improve seed quality. Using them, the effects of modifications
to the storage protein subunits can be rapidly evaluated before introducing
the mutated genes into plants.
