Posttranslational processing of concanavalin A precursors in jackbean cotyledons

Area of Science:

• Biochemistry
• Plant Molecular Biology

Background:

• Concanavalin A (ConA) is a well-studied lectin from jackbean.
• Understanding protein processing is crucial for cellular function and product development.

Purpose of the Study:

• To elucidate the intricate processing steps in the assembly of concanavalin A (ConA).
• To investigate the role of specific inhibitors and cellular compartments in ConA maturation.

Main Methods:

• Metabolic labeling with 14C-amino acids and pulse-chase experiments.
• Immunoprecipitation and analysis of lectin forms.
• Two-dimensional peptide mapping and NH2-terminal sequencing.
• Immunocytochemical studies with monensin treatment.

Main Results:

• Identified seven distinct intermediate species during ConA assembly.
• Demonstrated that ConA subunit formation involves reannealing of two fragments.
• Monensin inhibited precursor processing and induced secretion of ConA precursors.
• Processing occurred without significant refolding, activating carbohydrate-binding activity.

Conclusions:

• ConA assembly is a multi-step process involving proteolytic cleavage and fragment reannealing, potentially via transpeptidation.
• Monensin disrupts normal ConA trafficking and processing, highlighting the role of cellular compartments.
• The processing pathway is structurally compatible with the precursor and mature ConA tertiary structures.