SHEATHLIN - CLONING, CDNA POLYPEPTIDE SEQUENCES, AND IMMUNOLOCALIZATION OF PORCINE ENAMEL SHEATH PROTEINS/

Sheath proteins designate low-molecular-weight non-amelogenin enamel p olypeptides and their parent protein, which concentrate in the sheath space separating rod and interrod enamel (Uchida et al., 1995). Two po rcine sheath proteins, with apparent molecular weights of 13 and 15 kD a, are characterized by protein sequencing. The primary structures of these polypeptides match a portion of the derived amino acid sequences of clones isolated from a porcine enamel organ epithelia-specific cDN A library. Sheath protein RNA messages differ by the inclusion or dele tion of a 45-nucleotide segment and by the use of three alternative po lyadenylation/cleavage sites. The secreted proteins are 395 and 380 re sidues in length, with molecular masses of 42,358 and 40,279 Daltons a nd calculated isoelectric points of 6.3 and 6.7, respectively. Polyclo nal antibodies were raised against a synthetic peptide having the shea thlin-specific sequence EHETQQYEYSGGC. Immunohistochemistry with this antibody demonstrates that the protein encoded by the sheathlin cDNA i s preferentially localized in the sheath space. We propose that the po rcine sheath proteins and their proteolytic cleavage products be desig nated ''sheathlin''.