Interaction of diphtheria toxin with phosphorylated molecules

Area of Science:

• Biochemistry
• Cell Biology
• Toxicology

Background:

• Diphtheria toxin (DT) is a bacterial toxin that affects eukaryotic cells.
• The initial step in DT intoxication involves binding to specific cell surface receptors.

Purpose of the Study:

• To investigate the molecular nature of the diphtheria toxin binding site on cell surface glycoproteins.
• To identify compounds that inhibit the binding of diphtheria toxin to its cellular receptor.

Main Methods:

• Utilized 125I-labeled hamster thymocyte cell surface glycoproteins.
• Assessed the inhibitory effects of various nucleotides and phosphorylated compounds on toxin binding.
• Investigated direct binding of diphtheria toxin to phosphorylated proteins like casein.

Main Results:

• Nucleotides, particularly thymidine triphosphate, inhibited diphtheria toxin binding.
• Adenine-containing compounds showed dose-dependent inhibition, with tetraphosphate being most effective.
• Highly phosphorylated compounds (inositol hexaphosphate, casein, phosvitin) were potent inhibitors.
• Diphtheria toxin directly bound to phosphorylated casein, and this binding was reduced by alkaline phosphatase treatment.

Conclusions:

• Diphtheria toxin appears to bind to cell surface components with regions of high phosphate density.
• The cell surface receptor for diphtheria toxin may possess a polyanionic character.