A theoretical study on the specificity of tetramethylammonium versus monomethylammonium binding to the active site of a phosphorylcholine antibody.
In order to account for the specificity of binding of tetramethylammonium (TMA) versus monomethylammonium (MMA) to the combining site of phosphorylcholine specific immunoglobulin IgA H-8, theoretical computations are performed on the interaction energies of these cations with varying combinations of amino acid side chains, present or suspected to be present at that site. The dehydration of the cations, which represents a prerequisite for their binding is about 20 kcal/mol more difficult for MMA than for TMA. The interaction energies with the binding site are somewhat higher for MMA than for TMA. For some combinations of the amino acid side chains, their difference is smaller than the difference in the dehydration energy. Such combinations ensure preferential binding of TMA.
D000596:Amino Acids; D001666:Binding Sites, Antibody; D002794:Choline / Q000031:analogs & derivatives*; D007070:Immunoglobulin A / Q000378:metabolism*; D008744:Methylamines; D008956:Models, Chemical; D010767:Phosphorylcholine / Q000276:immunology*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D013816:Thermodynamics
D000596:Amino Acids; D007070:Immunoglobulin A; D008744:Methylamines; D000644:Quaternary Ammonium Compounds; D010767:Phosphorylcholine; C027451:methylamine; C027917:tetramethylammonium; D002794:Choline