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

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Abstract
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.