Degradation of β-Conglycinin β-Homotrimer by Papain: Independent Occurrence of Limited and Extensive Proteolysis

Abstract

Limited and extensive proteolysis occur when β-conglycinin β homo-trimer (β(3)-conglycinin) from soybeans is attacked by papain. Slow limited proteolysis is restricted to cleavage of β(3)-conglycinin polypeptides into subunit halves (N- and C-terminal domains) that are further slightly truncated. The kinetics of limited and extensive proteolyses analyzed separately indicates that the two processes occur independently from the very beginning of the reaction. In contrast, limited proteolysis of phaseolin from common beans has been found to be prerequisite for the onset of its extensive proteolysis. The dramatic distinction between the degradation patterns of β(3)-conglycinin and phaseolin, homologous storage 7S globulins, suggests the existence of intrinsic differences in their structures. This hypothesis is supported by comparative analysis of the accessibilities to the solvent of amino acid residues in phaseolin and β(3)-conglycinin structures, which indicated the relatively low packing density of the latter, resulting in enhanced susceptibility of it to extensive proteolysis.

11S storage globulin from pumpkin seeds: Regularities of proteolysis by papain

“…This is characteristic of both angiosperms and gymnosperms in accordance with all the available data. A slower but deeper degradation of storage globulin molecules by the cooperative mechanism may occur regardless of limited proteolysis as was shown to occur in vitro for oat 11S globulin [3] and soybean 7S globulin [8].…”

“…For instance, the packing density of soybean 7S globulin tertiary structure is relatively low. Therefore, its degradation follows the cooperative mechanism irrespective of the limited pro teolysis that also occurs independently, in parallel [8]. In contrast, the native common bean 7S globulin with a rel atively high packing density of its molecule [8] is inacces sible to cooperative proteolysis under the action of differ ent proteinases [9].…”

“…Therefore, its degradation follows the cooperative mechanism irrespective of the limited pro teolysis that also occurs independently, in parallel [8]. In contrast, the native common bean 7S globulin with a rel atively high packing density of its molecule [8] is inacces sible to cooperative proteolysis under the action of differ ent proteinases [9]. In this case, the onset of the cooper ative proteolysis is delayed and starts only after comple tion of limited proteolysis that generates a certain change in the 7S globulin tertiary structure [9].…”