Polypeptide ligation occurs during post-translational modification of concanavalin A

Area of Science:

• Biochemistry
• Molecular Biology
• Plant Science

Background:

• Lectins are proteins with carbohydrate-binding sites, crucial for various biological processes.
• Legume seeds, such as jack bean (Canavalia ensiformis), are abundant sources of lectins, including concanavalin A (Con A).
• Con A constitutes a significant portion of protein in jack bean cotyledons and exhibits unusual circular homology in its amino acid sequence.

Purpose of the Study:

• To elucidate the mechanism behind the observed circular homology in concanavalin A (Con A).
• To investigate whether genomic rearrangements or post-translational modifications are responsible for Con A's unique structure.
• To determine if this modification mechanism is novel in eukaryotic systems.

Main Methods:

• Amino acid sequencing of Con A and related legume lectins.
• Comparative sequence analysis to identify homology patterns.
• Investigating post-translational modifications of the initial polypeptide chain.

Main Results:

• The circular homology in Con A is not due to genomic rearrangements.
• A novel post-translational process involving polypeptide transposition and ligation was identified as the cause.
• This mechanism of circularization via post-translational modification is unprecedented in eukaryotes.

Conclusions:

• The circular structure of concanavalin A results from a unique post-translational modification.
• This finding challenges previous assumptions about lectin structure formation.
• The discovery opens new avenues for understanding protein modification in eukaryotes.