THE 100-KDA CHAIN OF NICEIN KALININ IS A LAMININ B2 CHAIN VARIANT/

We have isolated the basement membrane component nicein and performed rotary-shadow analyses using electron microscopy that showed the prese nce of two forms (I and II) of the protein. Molecular cloning of the c DNA that codes for the 100-kDa chain of the protein revealed that the sequence matches those independently identified for the 105-155-kDa su bunit of kalinin, a recently identified basement membrane component. T hese data demonstrate that nicein and kalinin contain an identical cha in. The length of the open reading frame in the cDNA (approximate to 5 200 nucleotides) and amino acid sequences obtained from the N-terminus of the 105-kDa kalinin chain showed the occurrence of a precursor pol ypeptide. This immature polypeptide is probably related to form I, obs erved by rotary shadowing, while the mature form is related to form II . It is noteworthy that nicein/kalinin subunits share discrete sequenc e similarities with the B2 chain of human laminin, but with a cleavage occurring within domain III that eliminates domains IV and V from the final product. The sequence of this subunit is nearly identical to th at of B2t, a recently described polypeptide supposed to be related to a new laminin variant. Since nicein/kalinin expression is specifically impaired in the severe genodermatosis Herlitz junctional epidermolysi s bullosa, the role and structure of this tissue-restricted laminin Va riant is crucial for the understanding of epidermal-dermal adhesion.