The C-terminus of the γ2 chain but not of the β3 chain of laminin-332 is indirectly but indispensably necessary for integrin-mediated cell reactions

Using a recombinant mini-laminin-332, we showed that truncation of the three C-terminal amino acids of the γ2 chain, but not of the C-terminal amino acid of the β3 chain, completely abolished α3β1 integrin binding and its cellular functions, such as attachment and spreading. However, a synthetic peptide mimicking the γ2 chain C-terminus did not interfere with α3β1 integrin binding or cell adhesion and spreading on laminin-332 as measured by protein interaction assays and electric cell-substrate impedance sensing. Nor was the soluble peptide able to restore the loss of integrin-mediated cell adhesiveness to mini-laminin-332 after deletion of the γ2 chain C-terminus. These findings spoke against the hypothesis that the γ2 chain C-terminus of laminin-332 is a part of the α3β1 integrin interaction site. In addition, structural studies with electron microscopy showed that truncation of the γ2 chain C-terminus opened up the compact supradomain structure of LG1–3 domains. Thus, by inducing or stabilizing an integrin binding–competent conformation or array of the LG1–3 domains, the γ2 chain C-terminus plays an indirect but essential role in laminin-332 recognition by α3β1 integrin and, hence, its cellular functions.