The LG1-3 Tandem of Laminin α5 Harbors the Binding Sites of Lutheran/Basal Cell Adhesion Molecule and α3β1/α6β1 Integrins

Abstract

The laminin-type globular (LG) domains of laminin ␣ chains have been implicated in various cellular interactions that are mediated through receptors such as integrins, ␣-dystroglycan, syndecans, and the Lutheran blood group glycoprotein (Lu). Lu, an Ig superfamily transmembrane receptor specific for laminin ␣5, is also known as basal cell adhesion molecule (B-CAM). Although Lu/B-CAM binds to the LG domain of laminin ␣5, the binding site has not been precisely defined. To better delineate this binding site, we produced a series of recombinant laminin trimers containing modified ␣ chains, such that all or part of ␣5LG was replaced with analogous segments of human laminin ␣1LG. In solid phase binding assays using a soluble Lu (Lu-Fc) composed of the Lu extracellular domain and human IgG1 Fc, we found that Lu bound to Mr5G3, a recombinant laminin containing ␣5 domains LN through LG3 fused to human laminin ␣1LG4 -5. However, Lu/B-CAM did not bind other recombinant laminins containing ␣5LG3 unless ␣5LG1-2 was also present. A recombinant ␣5LG1-3 tandem lacking the laminin coiled coil (LCC) domain did not reproduce the activity of Lu/B-CAM binding. Therefore, proper structure of the ␣5LG1-3 tandem with the LCC domain was essential for the binding of Lu/B-CAM to laminin ␣5. Our results also suggest that the binding site for Lu/B-CAM on laminin ␣5 may overlap with that of integrins ␣3␤1 and ␣6␤1.

The C-terminal Region of Laminin β Chains Modulates the Integrin Binding Affinities of Laminins

“…This situation has been in striking contrast to the interactions of collagens and ArgGly-Asp (RGD)-containing adhesive proteins with their integrin receptors, in which the amino acid residues that directly coordinate the divalent metal ions in the metal iondependent adhesion site of integrins, designated MIDAS, have been defined by x-ray crystallography (41,42). Several lines of evidence indicate that three LG domains, LG1-3, in laminin ␣ chains are prerequisites for the integrin binding activities of laminins (16,36,43,44). However, the ␣ chain monomers alone are functionally inactive (16 -19), thereby underscoring the importance of heterotrimerization of the ␣ chains with the ␤ and ␥ chains for laminin recognition by integrins.…”

Glycophorin-C sialylation regulates Lu/BCAM adhesive capacity during erythrocyte aging

“…[36][37][38][39][40] An initial study by Zen et al, using murine erythroleukemia cells expressing various Lu/BCAM domains, determined that the membrane proximal domain, domain 5, contributes to adhesion of these cells to laminin-a5. 38 Later, this finding was seemingly contradicted by 2 groups that used recombinant Lu/BCAM protein and BIACORE technology to address the same question.…”

Laminin-511 is an epithelial message promoting dermal papilla development and function during early hair morphogenesis

“…It is known that the integrin binding region lies in the G1-3 domain (Ido et al 2004;Nishiuchi et al 2006;Kikkawa et al 2007), while another region located in the G4-5 domain interacts with heparin sulfate proteoglycans (Yu and Talts 2003) such as perlecan, dystroglycan, or syndecans. To study the role of integrin binding with laminin-511's role in hair development, two purified recombinant laminin-511 molecules were tested, one with a deletion of the G4-5 domain of the ␣5 chain, which ablates the heparin binding, termed ⌬G4-5, and another termed ⌬G3-5, with a deletion of the G3-5 domain of the ␣5 chain, which removes both integrin and heparin binding.…”