Does an asparaginyl-specific cysteine endopeptidase trigger phaseolin degradation in cotyledons of kidney bean seedlings?
An asparaginyl-specific cysteine endopeptidase which was named ‘legumain-like proteinase’ (LLP) and has an apparent molecular mass of 38.1 kDa was isolated from cotyledons of kidney bean (Phaseolus vulgaris L.) seedlings and partially characterized. It is, to our knowledge, the first known proteinase which in vitro extensively degrades native phaseolin, the major storage globulin of this grain legume. Phaseolin that in vitro had been partially degraded by LLP (Pvitro) and phaseolin that was isolated after partial in vivo breakdown 6 days after the start of seed imbibition (Pvivo) showed similar fragment patterns on SDS/polyacrylamide gels. The fragments had identical cleavage sites in Pvitro and Pvivo as determined by partial amino acid sequencing. In both types of partially degraded phaseolin, these cleavage sites have asparagine in the P1 position. Two of the cleavage sites are located in the beta-barrel domain of the C-terminal module and only one cleavage site was found in the beta
