Sherblom A P, Sathyamoorthy N, Decker J M, Muchmore A V
Department of Biochemistry, University of Maine, Orono 04469.
J Immunol. 1989 Aug 1;143(3):939-44.
Utilizing a solid phase binding assay, we have demonstrated that rIL-2 binds with high affinity to the human urinary glycoprotein uromodulin. This binding is specifically inhibited by the saccharides diacetylchitobiose and Man(alpha 1-3)(Man(alpha 1-6]Man-O-methyl and by the high mannose glycopeptides Man5GlcNAc2-R and Man6GlcNAc2-R, but not by Man9GlcNAc2-R. rIL-2 also binds OVA, a glycoprotein which contains approximately 50% high mannose chains at a single glycosylation site, and to yeast mannan. This binding is inhibited by the same battery of saccharides which inhibit the binding to uromodulin. The conclusion that rIL-2 is a lectin is further supported by the observation that the sequence of IL-2 shares 27% homology with a 33-residue sequence of the carbohydrate-binding domain of human mannose-binding protein. The potential physiologic relevance of the carbohydrate binding activity is further elucidated by studies which show that 1) binding of soluble rIL-2 to immobilized uromodulin is enhanced at a pH of 4 to5 in the presence of divalent cations, and 2) neither uromodulin nor the high mannose glycopeptide Man5GlcNAc2Asn blocks the binding of rIL-2 to the IL-2R. Thus the carbohydrate-binding site of rIL-2 is distinct from the cell surface receptor-binding site, and might function preferentially in acidic microenvironments.
利用固相结合试验，我们已证明重组白细胞介素-2（rIL-2）与人类尿糖蛋白尿调节素具有高亲和力结合。这种结合被二乙酰壳二糖和Man(α1-3)[Man(α1-6)]Man-O-甲基等糖类以及高甘露糖糖肽Man5GlcNAc2-R和Man6GlcNAc2-R特异性抑制，但不被Man9GlcNAc2-R抑制。rIL-2还与卵清蛋白（OVA）结合，OVA是一种糖蛋白，在单个糖基化位点含有约50%的高甘露糖链，并且与酵母甘露聚糖结合。这种结合被抑制rIL-2与尿调节素结合的相同系列糖类所抑制。rIL-2是一种凝集素这一结论进一步得到如下观察结果的支持：白细胞介素-2的序列与人类甘露糖结合蛋白的碳水化合物结合结构域的33个残基序列具有27%的同源性。碳水化合物结合活性的潜在生理相关性通过以下研究进一步阐明：1）在二价阳离子存在下，可溶性rIL-2与固定化尿调节素的结合在pH为4至5时增强；2）尿调节素和高甘露糖糖肽Man5GlcNAc2Asn均不阻断rIL-2与白细胞介素-2受体（IL-2R）的结合。因此，rIL-2的碳水化合物结合位点与细胞表面受体结合位点不同，可能在酸性微环境中优先发挥作用。
