Expression of spasmolysin (FIM-A.1): an integumentary mucin from Xenopus laevis.
In the past, a unique type of precursor for a secretory protein was discovered. It contains a central repetitive domain rich in threonine residues and terminal cysteine-rich domains. Due to striking homologies of these terminal domains with pancreatic spasmolytic polypeptide, originally the name "prepro-spasmolysin" was proposed. Here we show that the mature protein has a MW of about 130 kDa, consisting of about 70% carbohydrate and 30% protein. Similar O-linked glycoproteins have been found in mucins from human intestine. For this and numerous other reasons we decided to rename this glycoprotein "frog integumentary mucin A.1" (FIM-A.1). Furthermore, analysis of the protein with specific antibodies against the predicted C-terminal end indicates that FIM-A.1 is probably not processed at pairs of basic residues. In situ hybridization as well as immunofluorescence studies revealed that FIM-A.1 is expressed and stored exclusively in mature mucous glands of Xenopus laevis skin. Only cone cells at the proximal part of these glands do not synthesize FIM-A.1. In contrast, all other physiologically active peptides from X. laevis skin investigated so far are synthesized in granular glands. A hypothetical function of FIMs for defense against microbial infections is discussed.
Max-Planck-Institut für Psychiatrie, Abteilung Neurochemie, Martinsried, Federal Republic of Germany.
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Hauser
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Gertzen
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D007106:Immune Sera; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009077:Mucins / Q000032:analysis / Q000235:genetics*; D009092:Mucous Membrane / Q000166:cytology; D015345:Oligonucleotide Probes; D009842:Oligopeptides / Q000138:chemical synthesis; D011993:Recombinant Fusion Proteins / Q000032:analysis; D012867:Skin / Q000166:cytology; D029867:Xenopus Proteins; D014982:Xenopus laevis
C064968:FIM-A.1 protein, Xenopus; D007106:Immune Sera; D009077:Mucins; D015345:Oligonucleotide Probes; D009842:Oligopeptides; D011993:Recombinant Fusion Proteins; D029867:Xenopus Proteins