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

Abstract

Limited proteolysis of the α- and β-chains and deep cleavage of the αβ-subunits by the cooperative (one-by-one) mechanism was observed in the course of papain hydrolysis of cucurbitin, an 11S storage globulin from seeds of the pumpkin Cucurbita maxima. An independent analysis of the kinetics of the limited and cooperative proteolyses revealed that the reaction occurs in two successive steps. In the first step, limited proteolysis consisting of detachments of short terminal peptides from the α- and β-chains was observed. The cooperative proteolysis, which occurs as a pseudo-first order reaction, started at the second step. Therefore, the limited proteolysis at the first step plays a regulatory role, impacting the rate of deep degradation of cucurbitin molecules by the cooperative mechanism. Structural alterations of cucurbitin induced by limited proteolysis are suggested to generate its susceptibility to cooperative proteolysis. These alterations are tentatively discussed on the basis of the tertiary structure of the cucurbitin subunit pdb|2EVX in comparison with previously obtained data on features of degradation of soybean 11S globulin hydrolyzed by papain.

Limited proteolysis initiates massive degradation of ginnacin, storage 11S globulin from Ginkgo seeds

“…The analysis of proteolysis kinetics was carried out following our previously described strategy (4,5). During mixed-type proteolysis, when limited and one-by-one proteolyses occur either in parallel independently from each other or successively, the input of the limited proteolysis in the total decline of the protein weight concentration of the hydrolyzate (P% 0 →P% t ) is equal to M% 0 -M% t .…”

“…The native soybean (4) and pumpkin (5) 11S globulins, and common bean 7S globulin (6) are initially inaccessible to the one-by-one proteolysis during proteinase action. Only after completion of limited proteolysis, resulting in regular alterations of their native structure, do soybean, pumpkin and common bean globulins acquire the ability for degradation by the one-by-one mechanism (4)(5)(6). Thus, the initial limited proteolysis plays a regulatory role, delaying the onset of the massive degradation of these storage proteins.…”