Lectin-binding domains on laminin

Abstract

The nature and location of carbohydrate moieties on the laminin molecule were identified by studying the binding affinity of a series of lectins for purified, proteasederived fragments of laminin. Laminin is a cross-shaped molecule containing three short arms (36 nm) and one long arm (76 nm). All arms contain globular end regions by electron microscopy. Purified fragments of laminin were obtained which (a) lacked the long arm of the molecule but retained the intact short arms, or (b) lacked both the long arm and the globular end regions of the short arms. These two types of fragments differed markedly in lectin-binding capacity. Using the known sugar specificities of the lectins and hapten sugar competition for lectin-binding to laminin fragments, the following conclusions were reached: (a) [alpha]--Galactopyranosyl end groups are markedly enriched in the globular end regions of the short arms compared to the rod-shaped portions of the molecule. (b) [alpha]--Mannopyranosyl residues are present on both the globular end regions and the rod-shaped portions of the molecule. (c) Exposed N-acetyl--galactosaminyl end groups are absent or present in low amounts on laminin. (d) (NANA)-(2 --> 6)-[beta]--Gal-(1 --> 4)-[beta]--GlcNAc-(1 --> 2)--Man-terminated oligosaccharide units are enriched on the rod-shaped regions of the short arms compared to the globular end regions.