THE PANCORNULINS - A GROUP OF SMALL PROLINE RICH-RELATED CORNIFIED ENVELOPE PRECURSORS WITH BIFUNCTIONAL CAPABILITIES IN ISOPEPTIDE BOND FORMATION

In this report, the pancornulins are identified as members of the spr (small, proline-rich) multigene family by amino acid sequence and mass spectrometry analyses, One of the pancornulins (14.9 kDa) is identica l to the protein predicted by spr-1 clone 128. The other pancornulins (16.9 kDa and 22 kDa) are novel members of the spr family, Immunoelect ron microscopy of purified cornified envelopes with a pancornulin-spec ific antibody established these proteins more definitively as cornifie d envelope precursors, In addition, two-dimensional electrophoretic an alyses of keratinocyte extracts labeled enzymatically with dansylcadav erine (to identify amine accepters) or dansylPGGQQIV (to identify amin e donors) showed that both glutamine and lysine residues within the pa ncornulins participate in the isopeptide linkage characteristic of cor nified envelope formation, These results contrasted with those obtaine d using involucrin, a prominent cornified envelope protein shown capab le of acting only as an amine acceptor in this system, Novel partial c DNAs obtained after reverse transcription and polymerase chain reactio n amplification of total messenger RNA with pancornulin-specific prime rs suggest that the spr multigene family may be even larger than previ ously described, The bifunctional reactivity of the pancornulins in cr oss-linking and the large number of family members identified to date suggest that the pancornulins and other spr-1-related proteins map be more important in cornified envelope formation than previously conside red, perhaps functioning as ''bridge'' molecules during the early phas es of cornified envelope assembly.