Human aglycosyl-IgG exhibits increased hydrophobicity: Binding/fluorescence studies with 8-anilinonaphthalene-1-sulfonic acid (ANS)

Abstract

Human monoclonal, aglycosyl-IgG produced in vitro in the presence of tunicamycin, was compared with its native and acid pH-altered counterparts for their respective abilities to bind the fluorescent hydrophobicity probe, 8-anilinonaphthalene sulfonate. A novel technique based on continous-flow dynamic dialysis (Sparrow et al., 1982, Anal. Biochem. 123:255–264) allowed binding studies under non-equilibrium conditions. While the native IgG conformation exhibits two, weak ANS binding sites (ca. 10 3 l/mol), aglycosyl-IgG has one weak and one moderate affinity (least squares average Ka = 2 × 10 4 l/mol) site, and the acid conformer binds yet another two ANS molecules with moderate affinity (4 × 10 4 l/mol). Increases in affinity and in the number of sites correlate roughly with increased relative percent fluorescence by conventional fluorimetry. The fluorescence lifetime of ANS bound to altered IgGs is about 10% longer (T 2 = 15 nsec by time-resolved fluorimetry) than that for native IgG. All populations also exhibit a rapid decay component (T 1 = 3 nsec) analogous to that seen for ANS in 50% aqueous dioxane. Results are discussed in relation to structural role(s) for IgG-linked heterosaccharides.