POSTTRANSLATIONAL PEPTIDE-BOND FORMATION DURING CONCANAVALIN-A PROCESSING IN-VITRO

Post-translational processing of concanavalin A (Con A) is complex, in volving deglycosylation, proteolytic cleavage on the carboxy group sid e of asparagine residues and formation of a peptide bond de novo. This has been studied with the I-125-labelled Con A glycoprotein precursor as a substrate for processing in vitro. Extracts of immature jackbean cotyledons and the commercially available purified preparation of asp araginylendopeptidase were able to catalyse the above processes. The p rocessing resulted in the conversion of the 33.5 kDa inactive glycopro tein precursor into an active lectin. Processing activity was maximal at approx. pH 5.5. Evidence to support processing at authentic sites w as obtained by observation of the release of I-125 at positions in the sequence where tyrosine residues were present.