Sialic acid-specific lectin from Tritrichomonas foetus

A novel sialic acid-specific lectin (TFL) was isolated from Tritrichomonas foetus culture supernatant and purified by erythrocyte adsorption followed by fetuin-agarose affinity chromatography. According to gel filtration TFL is a protein of 728 kDa, different from the two sialidases of 853 and 254 kDa, secreted by T. foetus into the medium. The lectin is formed by multimeric complexes of 66 kDa subunit according to SDS-PAGE under reducing conditions. TFL is glycosylated with 4.2% of carbohydrates, half of which is represented by glucose. The lectin reacts equally with N-acetyl and N-glycolyl neuraminic acid, free, in alpha 2,3- or alpha 2,6-linkage. TFL has 7-fold weaker affinity to alpha 2,8-linked N-acetylneuraminic acid (Neu5Ac) in colominic acid. Horse erythrocytes containing 4-O-acetyl Neu5Ac are agglutinated equally as compared to the human cells. TFL affinity to 9-O-acetyl Neu5Ac is 4-fold weaker as documented by hemagglutination inhibition with de-O-acetylated bovine submaxillary mucin, and ovine submaxillary mucin. A panel of mono- and oligosaccharides other than Neu5Ac do not inhibit TFL activity at 200 mM. The lectin does not require bivalent cations for activity, shows optimal reactivity at neutral pH and is stable at 4 degrees C. Anti-TFL antibodies identify membrane positivity on T. foetus, suggesting that the lectin functions in adhesion of the parasites. These findings, together with good stability and immunogenicity, make TFL a prospective candidate for further studies, especially in searching for efficient diagnostics and prevention of bovine trichomoniasis. (C) 1999 Elsevier Science B.V. All rights reserved.