IDENTIFICATION AND SEQUENCE-ANALYSIS OF 2 NEW MEMBERS OF THE SKALP ELAFIN AND SPAI-2 GENE FAMILY - BIOCHEMICAL-PROPERTIES OF THE TRANSGLUTAMINASE SUBSTRATE MOTIF AND SUGGESTIONS FOR A NEW NOMENCLATURE/

The human epithelial proteinase inhibitor SKALP/elafin and the porcine sodium-potassium ATPase inhibitor SPAI-2 are two highly homologous pr oteins that share an NH2-terminal transglutaminase substrate domain an d a COOH-terminal whey acidic protein (WAP) domain, Here we describe t he bovine and simian orthologs of SKALP/elafin as well as two new bovi ne family members that are designated Trappin-4 and Trappin-5 on the b asis of a new nomenclature that we propose (Trappin = TRansglutaminase substrate and WAP motif containing ProteIN). Sequence analysis of Tra ppin-4 and Trappin-5 revealed a domain structure that is very similar to SPAI-2 (Trappin-1) and SKALP/elafin (Trappin-2). The transglutamina se substrate motifs are conserved although the number of repeats varie s among species and among family members, The sequence of Trappin-4 an d Trappin-5 diverges from Trappin-1 and Trappin a at the putative reac tive site in the WAP domain, The bovine ortholog of Trappin a is expre ssed in tongue and snout epidermis; Trappin-4 is expressed in trachea, ileum, and tongue; and Trappin-5 is expressed at low levels in trache a, as determined by RNase protection and Northern blot analysis. Based on the analysis of 67 transglutaminase substrate repeats as present i n all known Trappin gene family members from four different mammalian species a consensus sequence could be established: Gly-Gln-Asp-Pro-Val -Lys (GQDPVK). Using biotinylated hexapeptide probes we found that the GQDPVK sequence is a very efficient transglutaminase substrate both f or guinea pig liver transglutaminase and for epidermal transglutaminas e, and it acts as acyl donor as well as acceptor, We propose that the Trappin protein family forms a new group of enzyme inhibitors with var ious specificities of the WAP domain, which share transglutaminase sub strate motifs that can act as an anchoring sequence.