Hydrophobically modified human IgG: Surface and biological activities

Hydrophobic modification of human IgG by fatty acid esters (C₈, C₁₂ and C₁₆) of N-hydroxysuccinimide was carried out. Such a modification leads to a spontaneous formation of micelle-like colloidal clusters with a mean diameter of 19.9-22.7 nm for C₈-modified IgG. C₁₂- and C₁₆-modified IgGs form larger clusters in spite of a lower number of attached alkyl chains. The adsorption of the modified IgGs onto latex particles was studied. It was found that the affinity of modified IgGs to the negatively charged hydrophobic polystyrene surface is higher than that of the native protein, although an increase in hydrophobicity is also followed by an increase in the net charge of the protein molecule. In all cases, the highest equilibrium concentrations correspond to the nearly saturated layer of adsorbed protein molecules, this layer being more compact for hydrophobized IgG. The molecular areas of IgGs on the surface are close to those calculated from the known structural data for the 'leg-on' disposition of the 'T'- or 'Y'-shaped molecules. The modified IgG retains high recognition ability in ELISA tests, the activity decreases only at a high degree of modification.