A cDNA encoding Tc-MUC-5, a mucin from Toxocara canis larvae identified byexpression screening

Toxocara canis is an ascarid nematode parasite of canids. Larvae infect a w ide range of accidental hosts including humans, in whom they are the aetiol ogic agent of visceral and ocular Larva migrans. The labile surface coat of T. canis larvae consists of a family of mucin glycoproteins termed TES-120 , for which the cDNAs have recently been cloned. In this paper, we describe the identification of a novel cDNA (Tc-muc-5) encoding an apomucin by expr ession screening of a cDNA library with antiserum raised to T. canis excret ory/secretory products, and compare the predicted Tc-MUC-5 protein with tho se of other T. canis mucins (Tc-MUC-1-Tc-MUC-4) that include the TES-120 su rface coat glycoproteins. Tc-MUC-5 has both a larger open reading frame and a more divergent sequence than the other T. canis mucins. It contains a pu tative signal peptide followed by two six-cysteine (SXC) domains, an extend ed threonine-rich central mucin core domain and two C-terminal SXC domains. Amino acid composition analysis of secreted TES-120 glycoproteins, reveale d a distinct lack of lysine residues; while this finding is in agreement wi th the primary sequences of Tc-MUC-1-Tc-MUC-4, Tc-MUC-5 is conspicuous by i ts relative abundance of lysines (6.7%), suggesting that this protein is no t part of the TES-120 family of surface coat proteins. (C) 2001 Elsevier Sc ience B.V. All rights reserved.