Low nidogen affinity of laminin‐5 can be attributed to two serine residues in EGF‐like motif γ2III4

High affinity nidogen binding of laminin-1 (chain composition α1β1γ1) has been previously mapped to a single EGF-like motif γ1III4 of its γ1 chain. Two more isoforms, laminin-5 (α3β3γ2) and laminin-7 (α3β2γ1), show low and high binding activity, respectively, indicating that the γ2 chain is of low affinity. This was confirmed by recombinant production of the homologous EGF-like motif γ2III4 of the γ2 chain, which has a 100,000-fold lower binding activity than γ1III4. The crucial heptapeptide binding sequence Asn-lle-Asp-Pro-Asn-Ala-Val of γ1III4 is modified in γ2III4 by replacing both the central Asn and Val by Ser. Changing these replacements to Asn and Val by site-directed mutagenesis enhanced the activity of γ2III4 to a level which was only 5-fold lower than that of γ1III4. Despite their high sequence identity (77%) motifs γ1III4 and γ2III4 were also shown to differ considerably in immunological epitopes. This indicates distinctly different functions for laminins which differ in the γ chain isoform.