Amyloids and Heparin
Amyloid proteins form fibers as they systematically stack in the presence of heparin. Examples of amyloids are the beta-amyloid and tau of Alzheimer’s disease, prions, and perhaps even sickle cell anemia fibers. Amyloids are proteins that stack into fibers and can be detected microscopically by binding particular stains, e.g. Congo Red. All of the amyloid proteins are also heparin binding, e.g. Alzheimer’s amyloid is 50% heparin sulfate. I surmise that the Congo Red is binding to the heparin-binding domains, because Congo Red also binds to cellulose and a particular lipopolysaccharide from Shigella flexneri. Antibodies and enzymes that bind to polysaccharides, bind through tryptophan residues that are flat, hydrophobic plates with regular spacing. The amyloid fibers presumably bind the broadly spaced hydrophobic surfaces of Congo Red by providing corresponding complementary hydrophobic regions of the basic amino acids that are grouped on the stacked amyloids. The interactions bet...