Concanavalin A is synthesized as a glycoprotein precursor

Area of Science:

• Plant biochemistry
• Molecular biology
• Protein chemistry

Background:

• Concanavalin A (Con A) is a lectin found in jack beans.
• Con A is synthesized as a precursor protein.
• Understanding Con A's post-translational modifications is crucial.

Purpose of the Study:

• To investigate the synthesis and processing of Con A.
• To characterize the oligosaccharide side chain of Con A.
• To elucidate the conversion of Con A precursor to mature Con A.

Main Methods:

• In vitro translation and in vivo pulse labeling of jack bean cotyledons.
• Analysis of protein molecular weight using gel electrophoresis.
• Glycosidase digestion of glycopeptides and gel filtration.

Main Results:

• Con A is synthesized as a 34,000 Mr polypeptide, with processing involving signal sequence removal and glycosylation.
• The oligosaccharide side chain of the Con A precursor is a high-mannose type.
• Pulse-chase experiments show the precursor (34,000 Mr) is converted to mature Con A (30,000 Mr) via glycopeptide removal.

Conclusions:

• Con A undergoes cotranslational processing, including glycosylation.
• The mature Con A structure results from the removal of a glycopeptide from its precursor.
• These modifications are discussed in relation to Con A's unique circular permutation.