LIMITED PROTEOLYSIS OF BETA-CONGLYCININ AND GLYCININ, THE 7S AND 11S STORAGE GLOBULINS FROM SOYBEAN [GLYCINE-MAX (L) MERR] - STRUCTURAL ANDEVOLUTIONARY IMPLICATIONS

The G2 (A2B1a) glycinin subunit from soybean (Glycine max L. Merr.) wa s purified and renatured to the homohexameric holoprotein. This protei n along with purified beta-conglycinin were subjected to limited prote olysis by trypsin. The generated polypeptide fragments were separated via SDS/PAGE and the amino acid sequence of the N-terminals was determ ined. Four cleavage points were detected in the alpha-chain A2 of glyc inin as well as in the alpha'-chain of beta-conglycinin. From the know n three-dimensional structure of 7S globulin and the hypothetical mode l of 7S globulin-like 11S globulin structure, it was possible to draw the conclusion that two distinct types of susceptible sites for proteo lytic cleavage are characteristic of the subunits of both globulins. T he first includes the sequences linking N- and C-terminal domains of b oth globulins and the sequence of N-terminal extensions of 70-kDa subu nits from the vicilin-like 7S globulins. The second type includes the loop between beta-strands E and F of the N-terminal domain of 11S glob ulins and of the C-terminal domain of 7S globulins. A statistically si gnificant similarity was found between the N-terminal extension of the alpha'-chain of beta-conglycinin and the interdomain linker regions o f soybean glycinin and pea legumin. It is proposed that the three sequ ence regions which form the first type of susceptible sites are of sim ilar structural function and might have evolved from the N-terminal se gment of a putative single-domain ancestor.