SIMILARITIES OF INTEGUMENTARY MUCIN B.1 FROM XENOPUS-LAEVIS AND PREPRO-VON WILLEBRAND FACTOR AT THEIR AMINO-TERMINAL REGIONS

Frog integumentary mucin B.1 (FIM-B.1) contains various cysteine-rich modules. In the past, a COOH-terminal ''cystine knot'' motif has been found that is similar to von Willebrand factor; this region is general ly known to be responsible for dimerization processes. Furthermore, a ''complement control protein'' motif is present as an internal cystein e-rich domain in FIM-B.1. We characterize here the missing 75% toward the NH2 terminus of the FIM B.1 precursor by molecular cloning. Analog ous to prepro-von Willebrand factor, four elements with considerable s imilarity to D-domains are present (i.e. D1-D2-D'-D3). These domains h ave been described as essential for the multimerization of von Willebr and factor. Thus, the general structure of FIM-B.1 resembles that of t he human mucin MUC2 as well as prepro-von Willebrand factor; these thr ee molecules at least seem to share common structural elements allowin g similar multimerization mechanisms.