Identification and proteolytic processing of procardosin A

摘要: Plant aspartic proteinases contain a plant-specific insert (PSI) of about 100 amino acids unknown function with no similarity the other but significant saposins, animal sphingolipid activator proteins. PSI has remained elusive at protein level, suggesting that it may be removed during processing. To understand molecular relevance PSI, proteolytic processing cardosin A, major proteinase from flowers cardoon (Cynara cardunculus L.) was studied. Procardosin 64-kDa A precursor containing and prosegment identified by immunoblotting using monospecific antibodies against prosegment. undergoes as flower matures. found to before prosegment, indicating enzyme acquires structure typical mammalian or microbial proforms. In vitro studies showed occurs pH 3.0 is inhibited pepstatin 7.0. Sequence analysis allowed identification cleavage sites, revealing entirely, probably an proteinase. Cleavage scissile bonds requires, however, conformation specific since isolated cardosins pistil extracts were unable hydrolyse synthetic peptides corresponding sites. view these results, model for proposed physiological in plant discussed.