γ2 Chain of laminin-5 is recognized by monoclonal antibody GB3

Abstract

Herlitz junctional epidermolysis bullosa is an autosomal recessive disorder characterized by generalized blistering at the lamina lucida of the cutaneous basement membrane. The monoclonal antibody GB3 has been used as a diagnostic probe because of its lack of reactivity in patient skin. The antigen recognized by GB3 has been identified as laminin-5, a glycoprotein consisting of three subunits (α3, β3 and γ2). To identify the laminin-5 protein chain that contains the epitope recognized by GB3 and to determine if chain assembly is required for antibody recognition, we expressed a γ2 protein constructed from a full-length γ2 cDNA. Radioimmunoprecipitation of the culture medium from 293 cells revealed that both GB3 and anti-γ2 polyclonal antibodies were capable of directly precipitating recombinant γ2 without coprecipitation of other proteins. In immunodepletion experiments, each antibody removed most of the protein that was reactive with the other antibody. The epitope recognized by GB3 is present only when the complex is in the native conformation because GB3 reacted only with the non-reduced laminin-5, but not the reduced laminin-5 in immunoblots. Moreover, because GB3 reacted with laminin-5 of SCC25 cells (γ2 in the heterotrimer) but not recombinant γ2 in 293 cells (γ2 alone) during indirect immunofluoresence staining, this epitope may be dependent upon a less stable conformation of γ2. We conclude that GB3 recognizes the γ2 chain of laminin-5 and that the epitope is entirely contained in the native form of the γ2 chain.