Integrin and neurocan binding to L1 involves distinct Ig domains.
The cell adhesion molecule L1, a 200-220-kDa type I membrane glycoprotein of the Ig superfamily, mediates many neuronal processes. Originally studied in the nervous system, L1 is expressed by hematopoietic and many epithelial cells, suggesting a more expanded role. L1 supports homophilic L1-L1 and integrin-mediated cell binding and can also bind with high affinity to the neural proteoglycan neurocan; however, the binding site is unknown. We have dissected the L1 molecule and investigated the cell binding ability of Ig domains 1 and 6. We report that RGD sites in domain 6 support alpha5beta1- or alphavbeta3-mediated integrin binding and that both RGD sites are essential. Cooperation of RGD sites with neighboring domains are necessary for alpha(5)beta(1). A T cell hybridoma and activated T cells could bind to L1 in the absence of RGDs. This binding was supported by Ig domain 1 and mediated by cell surface-exposed neurocan. Lymphoid and brain-derived neurocan were structurally similar. We also present evidence that a fusion protein of the Ig 1-like domain of L1 can bind to recombinant neurocan. Our results support the notion that L1 provides distinct cell binding sites that may serve in cell-cell or cell-matrix interactions.
Oleszewski
M
M
Tumor Immunology Programme, G0100, German Cancer Research Center, D-69120 Heidelberg, Germany.
Beer
S
S
Katich
S
S
Geiger
C
C
Zeller
Y
Y
Rauch
U
U
Altevogt
P
P
D000818:Animals; D001665:Binding Sites; D002412:Cations / Q000378:metabolism; D011508:Chondroitin Sulfate Proteoglycans / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006026:Glycoside Hydrolases / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D006825:Hybridomas / Q000378:metabolism; D007136:Immunoglobulins / Q000737:chemistry; D016023:Integrins / Q000378:metabolism*; D037181:Lectins, C-Type; D039841:Leukocyte L1 Antigen Complex; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D019006:Neural Cell Adhesion Molecules / Q000235:genetics / Q000378:metabolism*; D058580:Neurocan; D009842:Oligopeptides / Q000737:chemistry / Q000235:genetics; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism
D002412:Cations; D011508:Chondroitin Sulfate Proteoglycans; D007136:Immunoglobulins; D016023:Integrins; D037181:Lectins, C-Type; D039841:Leukocyte L1 Antigen Complex; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D019006:Neural Cell Adhesion Molecules; D058580:Neurocan; D009842:Oligopeptides; D011994:Recombinant Proteins; C076817:NCAN protein, human; C047981:arginyl-glycyl-aspartic acid; D006493:Heparin; D006026:Glycoside Hydrolases; C020668:glycanase