Carbohydrate-binding specificity of pokeweed mitogens

Area of Science:

• Immunology
• Glycobiology
• Biochemistry

Background:

• Pokeweed mitogens (Pa-1 and Pa-2) are plant lectins known to interact with cell surface carbohydrates.
• Understanding the specific binding interactions of these mitogens is crucial for elucidating their biological functions and potential applications.

Purpose of the Study:

• To determine the carbohydrate-binding specificity of pokeweed mitogens Pa-1 and Pa-2.
• To identify the specific receptors for these mitogens on human erythrocytes.

Main Methods:

• Hemagglutination inhibition assays were performed.
• Quantitative inhibition assays using radiolabeled lectins and various carbohydrate inhibitors were conducted.
• Affinity chromatography using immobilized mitogens (Pa-1-Sepharose 4B and Pa-2-Sepharose 4B) was employed to isolate receptors.

Main Results:

• Chitin oligosaccharides and glycoproteins like PAS-1 and band-3 glycoprotein strongly inhibited mitogen binding.
• Band-3 glycoprotein exhibited high affinity for both Pa-1 and Pa-2, with binding constants similar to mitogen-erythrocyte association constants.
• Competitive binding studies indicated that Pa-1 and Pa-2 share common binding sites on erythrocyte surface oligosaccharides.
• Affinity chromatography confirmed band-3 glycoprotein as the primary binding molecule for both mitogens.

Conclusions:

• Pokeweed mitogens Pa-1 and Pa-2 possess similar carbohydrate-binding specificities.
• These mitogens primarily bind to the sugar chains of band-3 glycoprotein on human erythrocytes, likely recognizing a di-N-acetylchitobiose moiety within the core structure.