Practice question

Acidic character gangliosides derives sialic acid carboxylate not phosphate sulfate fatty acid groups. N acetylneuraminic acid NANA nine carbon sugar pKa about two point six due alpha keto acid carboxyl fully ionized pH seven point four conferring net negative charge and electrophoretic mobility. Monosialoganglioside GM1 carries one charge disialo GD1a two trisialo GT1b three tetra GT1c four enabling separation DEAE anion exchange thin layer chromatography migration anode toward positive electrode. Charge influences calcium bridging modulation binding extracellular matrix proteins complement factor H myelin associated glycoprotein via siglec interactions sialic acid recognizing immunoglobulin lectins and neuronal excitability. Phosphate contributes PS PI anionic nature sulfate sulfatide three O sulfogalactosylceramide but gangliosides rely exclusively sialic acid for acidity. Sialyltransferases ST3GAL5 ST8SIA ST6GAL family in Golgi add Neu5Ac using CMP Neu5Ac donor high energy nucleotide sugar. Understanding sialic acid charge explains ganglioside immunogenicity receptor function electrophoretic patterns and why desialylation neuraminidase abolishes cholera toxin binding reducing negative surface potential affecting signaling and pathogen shielding examined in biochemistry and neurochemistry.