NECTINEPSIN - A NEW EXTRACELLULAR-MATRIX PROTEIN OF THE PEXIN FAMILY - CHARACTERIZATION OF A NOVEL CDNA-ENCODING A PROTEIN WITH AN RGD CELL-BINDING MOTIF

We report the isolation and characterization of a novel cDNA from quai l neuroretina encoding a putative protein named nectinepsin. The necti nepsin cDNA identifies a major 2,2-kilobase mRNA that is detected from ED 5 in neuroretina and is increasingly abundant during embryonic dev elopment. A nectinepsin mRNA is also found in quail liver, brain, and intestine and in mouse retina. The deduced nectinepsin amino acid sequ ence contains the RGD cell binding motif of integrin ligands. Furtherm ore, nectinepsin shares substantial homologies with vitronectin and st ructural protein similarities with most of the matricial metalloprotea ses. However, the presence of a specific sequence and the lack of hepa rin and collagen binding domains of the vitronectin indicate that nect inepsin is a new extracellular matrix protein. Furthermore, genomic So uthern blot studies suggest that nectinepsin and vitronectin are encod ed by different genes. Western blot analysis with an anti-human vitron ectin antiserum revealed, in addition to the 65- and 70-kDa vitronecti n bands, an immunoreactive protein of about 54 kDa in all tissues cont aining nectinepsin mRNA. It seems likely that the form of vitronectin found in chick egg yolk plasma by Nagano et al. ((1992) J. Biol. Chem. 267, 24863-24870) is the protein that corresponds to the nectinepsin cDNA. This new protein could be an important molecule involved in the early steps of the development.