Purification and basic characteristics of sialidase from Tritrichomonas mobilensis

Sialidase, produced by Tritrichomonas mobilensis, a colonic parasite of squirrel monkeys, was purified by adsorption on human RBCs in ice-cold culture supernatant followed by release in PBS at 37 degrees C. The enzyme was purified by size-exclusion chromatography of RBC-eluted material giving a single peak with sialidase activity of molecular weight approx. 630 kDa, representing a quadrimer of the complex of three subunits. SDS-PAGE under reducing conditions showed three bands of 56, 61, and 66 kDa, identical with the molecular weight of the three subunits of T. mobilensis sialic acid-specific lectin (Babál et al., 1994). The enzyme treatment changed the agglutination of human RBCs by other lectins: created agglutinability with galactose-specific peanut agglutinin, but did not change agglutination with alpha 2,6 sialic acid linkage-specific Sambucus nigra lectin and linkage nonspecific TML. A 4-fold decrease of the agglutination with alpha 2,3 sialic acid linkage-specific Maackia amurensis lectin was observed. Histochemistry of kidney glomeruli after T. mobilensis sialidase treatment showed peanut agglutinin positivity on membranes of podocytes indicating selectivity for alpha 2,3 linked sialic acid. The sialidase did not hydrolyze colominic acid and was inhibited by 2,3-dehydro-2-deoxy-NeuAc. Divalent cations were not required for activity. The enzyme activity was optimal at pH 6.5-7 with RBCs as substrate and could be stored for 1 year at 4 degrees C.