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A short interdomain sequence between the N- and Cterminal domains of b-conglycinin, the major 7S seed storage protein of soybean, was selected as a target for insertion of amino acid residues specifically cleaved by an asparaginyl endopeptidase that processes 11S globulins into acidic and basic chains. Modified b- conglycinin subunits containing the proteolytic cleavage site self-assembled into trimers in vitro at an efficiency similar to that of the unmodified subunit. In contrast to the absence of cleavage of the unmodified subunits, however, the modified b-conglycinin trimers were processed by purified soybean asparaginyl endopeptidase into two polypeptides, each the size expected for the b-conglycinin N- and C-terminal domains, respectively. The cleavage did not alter the assembly of mutant b-conglycinins and the cleaved mutant trimers remained stable to further proteolytic attack. To examine the possibility of coassembly between the cleaved 11S and 7S subunits, in vitro processed mutant b-conglycinin subunits were mixed with native dissociated 11S globulin preparations. Reassembly at a high ionic condition did not induce the 7S subunits to interact with 11S subunits to form hexameric complexes. Thus, cleavage of 7S globulin subunits into acidic and basic domains may not be sufficient for hexamer as-


A short interdomain sequence between the N- and Cterminal domains of b-conglycinin, the major 7S seed storage protein of soybean, was selected as a target for insertion of amino acid residues specifically cleaved by an asparaginyl endopeptidase that processes 11S globulins into acidic and basic chains. Modified b- conglycinin subunits containing the proteolytic cleavage site self-assembled into trimers in vitro at an efficiency similar to that of the unmodified subunit. In contrast to the absence of cleavage of the unmodified subunits, however, the modified b-conglycinin trimers were processed by purified soybean asparaginyl endopeptidase into two polypeptides, each the size expected for the b-conglycinin N- and C-terminal domains, respectively. The cleavage did not alter the assembly of mutant b-conglycinins and the cleaved mutant trimers remained stable to further proteolytic attack. To examine the possibility of coassembly between the cleaved 11S and 7S subunits, in vitro processed mutant b-conglycinin subunits were mixed with native dissociated 11S globulin preparations. Reassembly at a high ionic condition did not induce the 7S subunits to interact with 11S subunits to form hexameric complexes. Thus, cleavage of 7S globulin subunits into acidic and basic domains may not be sufficient for hexamer as-