Characterization of a new calcium-binding protein abundant in amniotic fluid, CAAF2, which is produced by fetal epidermal keratinocytes during embryogenesis.

By using a 45Ca2+ overlay technique, we found two calcium-binding proteins (CaBPs) abundant in bovine amniotic fluid, and named them CAAF1 (calcium-binding protein in amniotic fluid-1) and CAAF2. CAAF1 was identified as a novel S100 protein produced by fetal epidermal keratinocytes, squamous epithelial cells and polymorphonuclear leukocytes. Here, we report the primary structure and the tissue distribution of bovine CAAF2. CAAF2 is a newly isolated protein with the two EF hand motifs peculiar to S100 proteins, and 29.7% homology to CAAF1. CAAF2 is 63.4% homologous to human psoriasin, a S100 protein up-regulated in psoriatic epidermis. Northern blot analysis demonstrates that CAAF2 is unique in that it is exclusively expressed in the epidermis. Our results suggest that the majority of CaBPs in amniotic fluid consist of two distinct S100 proteins, CAAF1 and CAAF2, which are produced by fetal epidermal keratinocytes.