The complete primary structure of abrin-a B chain

Area of Science:

• Molecular Biology
• Protein Chemistry
• Toxicology

Background:

• Abrin is a potent toxin found in the seeds of Abrus precatorius.
• Understanding the precise structure of abrin is crucial for developing antitoxins and studying its mechanism of action.
• Previous studies relied on nucleotide sequencing, which may not fully capture protein isoforms.

Purpose of the Study:

• To determine the complete 267 amino acid sequence of the abrin-a B chain.
• To identify potential isoforms of abrin.
• To compare the abrin-a B chain sequence with that of ricin-D B chain.

Main Methods:

• Peptide analysis following enzymatic digestion of abrin-a B chain.
• Enzymes used included trypsin, chymotrypsin, lysyl endopeptidase, Staphylococcus aureus V8 protease, and thermolysin.
• Amino acid sequencing of resulting peptides.

Main Results:

• The complete amino acid sequence of abrin-a B chain was elucidated.
• The determined sequence differed from predictions based on nucleotide sequencing, suggesting the existence of abrin isoforms.
• A high sequence identity (59%) was observed between abrin-a B chain and ricin-D B chain.
• Abrin-a B chain exhibits a domain structure with subdomains of approximately 40 amino acids.

Conclusions:

• The direct amino acid sequencing confirms the structure of abrin-a B chain and highlights the presence of isoforms.
• The significant sequence homology between abrin and ricin B chains suggests a common evolutionary origin and conserved function.
• The identified domain structure provides a basis for understanding abrin's molecular interactions and biological activity.