We report the identification of a novel laminin variant that appears to be unique to a subset of epithelial basement membranes. The variant contains two chains electrophoretically and immunologically identical to the B1 and B2 chains. Epitopes contained in the laminin A chain are absent from the molecule, and a 190-kD chain substitutes for the A chain. V8 protease analysis and Western blotting studies indicate that the variant 190-kD chain shows structural and immunological similarity to the 200-kD chain of kalinin. Rotary shadowing analysis indicates that the 190-kD chain contributes a large globular structure to the variant long arm, but lacks the short arm contributed to laminin by the A chain. The variant is produced by cultured skin explants, human keratinocytes and a squamous cell carcinoma line, and is present in human amniotic fluid. Polyclonal antibodies raised to kalinin, a recently characterized novel component of anchoring filaments, and mAb BM165 which recognizes a subunit of kalinin (Rousselle et al., 1991) cross react with the variant under nonreducing conditions. Immunohistological surveys of human tissues using the crossreacting antikalinin antiserum indicate that the distribution of this laminin variant is at least restricted to anchoring filament containing basement membranes. We propose the name K-laminin for this variant.

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