Cell type-specific differences in glycosaminoglycans modulate the biological activity of a heparin-binding peptide (RKRLQVQLSIRT) from the G domain of the laminin alpha 1 chain

AG73 (RKRLQVQLSIRT), a peptide from the G domain of the laminin alpha1 chai n, has diverse biological activities with different cell types, The heparan sulfate side chains of syndecan-1 on human salivary gland cells were previ ously identified as the cell surface ligand for AG73. We used homologous pe ptides from the other laminin cu-chains (A2G73-A5G73) to determine whether the bioactivity of the AG73 sequence is conserved. Human salivary gland cel ls and a mouse melanoma cell line (B16F10) both bind to the peptides, but c ell attachment was inhibited by glycosaminoglycans, modified heparin, and s ized heparin fragments in a cell type-specific manner. In other assays, AG7 3, but not the homologous peptides, inhibited branching morphogenesis of sa livary glands and B16F10 network formation on Matrigel. We identified resid ues critical for AG73 bioactivity using peptides with amino acid substituti ons and truncations. Fewer residues were critical for inhibiting branching morphogenesis (XKXLXVXXXIRT) than those required to inhibit B16F10 network formation on Matrigel (N-terminal XxRLQVQLSIRT). In addition, surface plasm on resonance analysis identified the C-terminal IRT of the sequence to be i mportant for heparin binding. Structure based sequence alignment predicts A G73 in a P-sheet with the N-terminaI K (Lys(2)) and the C-terminal R (Arg(1 0)) on the surface of the G domain. In conclusion, we have determined that differences in cell surface glycosaminoglycans and differences in the amino acids in AG73 recognized by cells modulate the biological activity of the peptide and provide a mechanism to explain its cell-specific activities.