A Family of Secreted Mucins from the Parasitic Nematode Toxocara canis Bears Diverse Mucin Domains but Shares Similar Flanking Six-cysteine Repeat Motifs

• Published in: The Journal of biological chemistry 2000-12, Vol.275 (50), p.39600-39607
• Main Authors: Loukas, Alex, Hintz, Martin, Linder, Dietmar, Mullin, Nicholas P., Parkinson, John, Tetteh, Kevin K.A., Maizels, Rick M.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; apomucin; Blotting, Western; Chromatography; Chromatography, High Pressure Liquid; Cysteine - chemistry; DNA, Complementary - metabolism; Electrophoresis, Polyacrylamide Gel; Expressed Sequence Tags; Female; Gastric Mucins - chemistry; Gastric Mucins - genetics; Gene Library; Models, Biological; Models, Molecular; Molecular Sequence Data; mucin; Mucins - chemistry; Mucins - genetics; Multigene Family; Protein Sorting Signals; Protein Structure, Tertiary; Recombinant Proteins - metabolism; RNA, Messenger - metabolism; Sequence Homology, Amino Acid; Serine - chemistry; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Tc-MUC-1 gene; Tc-MUC-2 gene; Tc-MUC-3 gene; TES-120 protein; Threonine - chemistry; Toxocara canis; Toxocara canis - chemistry
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M005632200

Infective larvae of the parasitic nematodeToxocara canis secrete a family of mucin-like glycoproteins, which are implicated in parasite immune evasion. Analysis of T. canis expressed sequence tags identified a family of four mRNAs encoding distinct apomucins (Tc-muc-1–4), one of which had been previously identified in the TES-120 family of glycoproteins secreted by this parasite. The protein products of all four cDNAs contain signal peptides, a repetitive serine/threonine-rich tract, and varying numbers of 36-amino acid six-cysteine (SXC) domains. SXC domains are found in many nematode proteins and show similarity to cnidarian (sea anemone) toxins. Antibodies to the SXC domains of Tc-MUC-1 andTc-MUC-3 recognize differently migrating members of TES-120. TES-120 proteins separated by chromatographic methods showed distinct amino acid composition, mass, and sequence information by both Edman degradation and matrix-assisted laser desorption ionization/time of flight mass spectrometry on peptide fragments. Tc-MUC-1, -2, and -3 were shown to be secreted mucins with real masses of 39.7, 47.8, and 45.0 kDa in contrast to their predicted peptide masses of 15.7, 16.2, and 26.0 kDa, respectively. The presence of SXC domains in all mucin products supports the suggestion that the SXC motif is required for mucin assembly or export. Homology modeling indicates that the six-cysteine domains of the T. canis mucins adopt a similar fold to the sea anemone potassium channel-blocking toxin BgK, forming three disulfide bonds within each subunit.