Massa S M, Cooper D N, Leffler H, Barondes S H
Department of Psychiatry, University of California, San Francisco 94143.
Biochemistry. 1993 Jan 12;32(1):260-7. doi: 10.1021/bi00052a033.
The soluble mammalian lactose-binding lectins L-14-I and L-29 are both secreted and bind to oligosaccharides on laminin, a large extracellular matrix glycoprotein containing polylactosamine chains. Because of the potential functional significance of these lectin-laminin interactions, we compared quantitative aspects of L-14-I and L-29 binding to immobilized laminin using recombinant lectins labeled with 125I. We report that the concentration-dependent binding of L-29 exhibits positive cooperativity whereas binding of L-14-I does not. Cooperative binding of L-29 can also occur on glycoconjugate substrates other than laminin and is not dependent on cystine bond formation or aggregation in solution. L-29 contains repetitive sequences within the N-terminal domain not present in L-14-I. This domain is not required for binding activity, but is required for positive cooperativity. Though the precise mechanism of interaction of L-29 with laminin remains to be determined, it apparently results in assembly of a lectin aggregate on the substrate surface, which could have important functional consequences.
可溶性哺乳动物乳糖结合凝集素L-14-I和L-29既可以分泌，又能与层粘连蛋白上的寡糖结合。层粘连蛋白是一种含有聚乳糖胺链的大型细胞外基质糖蛋白。鉴于这些凝集素与层粘连蛋白相互作用可能具有功能上的重要意义，我们使用用125I标记的重组凝集素，比较了L-14-I和L-29与固定化层粘连蛋白结合的定量情况。我们报告称，L-29的浓度依赖性结合表现出正协同性，而L-14-I的结合则没有。L-29的协同结合也可以发生在除层粘连蛋白之外的糖缀合物底物上，并且不依赖于胱氨酸键的形成或溶液中的聚集。L-29在N端结构域中含有L-14-I中不存在的重复序列。该结构域对于结合活性不是必需的，但对于正协同性是必需的。虽然L-29与层粘连蛋白相互作用的确切机制仍有待确定，但它显然会导致凝集素聚集体在底物表面组装，这可能会产生重要的功能后果。
