Functional role of sialic acid in IgG binding to microvillus membranes in neonatal rat intestine.
A close parallelism exists between sialylation and endocytotic activity of the small intestine during postnatal development in rats. Thus, the binding of 125I-labelled IgG to microvillus membranes and its relationship to membrane sialic acid has been studied in suckling rat intestine, during (a) postnatal development; (b) cortisone-induced precocious maturation, and (c) after desialylation of brush borders by neuraminidase treatment. Neuraminidase-treated membranes exhibited low (42%, p < 0.001) IgG binding. The observed decrease in IgG binding to desialylated membranes was associated with a decrease in the value of affinity constant, (-Ka = 0.4 x 10(6) M-1 in control and 0.23 x 10(6) M-1 in desialylated membranes). The number of IgG-binding sites (2.3 nmol/mg protein) was unchanged under these conditions. A similar decrease (50%) in IgG binding to brush borders was also observed in cortisone-injected pups. This was associated with reduced sialic acid (37%) content of the membranes compared to the controls. The value of -Ka was reduced from 0.4 x 10(6) M-1 in the control to 0.3 x 10(6) M-1 in the hormone-injected pups. The number of binding sites (n) was decreased from 2.2 to 1.4 nmol/mg protein under these conditions. Low concentrations of calcium (0.1-1.6 mM) in the incubation medium enhanced IgG binding (p < 0.001) to brush borders in pups but there was no change in binding of IgG to the membranes at 2 mM Ca2+ concentration compared to controls. Addition of Zn2+ or Mg2+ did not affect IgG binding under these conditions. These findings suggest a functional role of Ca2+ and sialic acid residues of the membrane glycans in IgG-receptor interactions in suckling rat intestine.
Gill
R K
RK
Department of Biochemistry, Panjab University, Post-Graduate Institute of Medical Education and Research, Chandigarh, India.
Mahmood
S
S
Nagpaul
J P
JP
Mahmood
A
A
D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D007074:Immunoglobulin G / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007477:Ions; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D008670:Metals / Q000737:chemistry / Q000494:pharmacology; D008871:Microvilli / Q000378:metabolism; D019158:N-Acetylneuraminic Acid / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar
D007074:Immunoglobulin G; D007477:Ions; D008670:Metals; D019158:N-Acetylneuraminic Acid