Expression and functional properties of genetically engineered ricin B chain lacking galactose-binding activity

Area of Science:

• Biochemistry
• Molecular Biology
• Toxicology

Background:

• Ricin is a toxic protein from Ricinus communis, composed of A and B subunits.
• The B chain acts as a lectin, binding to galactose residues.
• Previous studies identified critical residues for galactose binding in the B chain.

Purpose of the Study:

• To investigate the role of the high-affinity galactose-binding site in ricin B chain function.
• To determine the impact of mutating Asn-255 on ricin's lectin activity and cytotoxicity.

Main Methods:

• Oligonucleotide-directed mutagenesis was used to alter Asn-255 to Ala-255 in the ricin B chain.
• The mutant ricin B chain was expressed in Cos-M6 cells.
• Lectin activity and cytotoxicity of the wild-type and mutant A-B heterodimers were assessed.

Main Results:

• A single mutation from Asn-255 to Ala-255 in the ricin B chain was confirmed.
• The mutant B chain formed A-B heterodimers comparable to the wild-type.
• The Asn-255 to Ala-255 mutation resulted in a >99% loss of lectin activity and cytotoxicity.

Conclusions:

• The Asn-255 residue is critical for the high-affinity galactose binding of ricin B chain.
• Altering this residue abrogates ricin's lectin activity and cytotoxicity.
• This research deepens the understanding of ricin's molecular mechanisms and potential targets for intervention.