A heterogeneous polysaccharide (PS) was isolated from the venom of the tropical ant Pseudomyrmex sp. which activates the classical complement (C) pathway. Six sugars were identified in the PS by gas chromatography, and the molar ratios were determined. The 'sugars are mannose, N-acetylglucosamine, galactose, fucose, N-acetylgalactosamine, and glucose. A small PS, estimated to have a mol. wt of 3000 daltons on Sephadex G-25, was separated from a larger species, and may be a cleavage product of the larger PS. Both species were potent activators of the classical C pathway. The large and small PS have a strong net negative charge because of hexuronic acid(s), and both bind mainly to β-lipoprotein in serum to form a visible precipitate. Precipitation is prevented by ethylenediaminetetraacetate. partially prevented by 300 mM NaCl, but not prevented by heating the serum at 56° C for 30 min. It is not certain if binding to β-lipoprotein is an absolute necessity for C1 activation and the resulting C4 and C2 consumption. The PS caused C4 and C2 consumption in a serum deficient in apolipoprotein B, but no visible precipitation was observed. In studies of the mechanism of C1 activation. 125I-C1q could not be shown to bind to the PS or to PS-β-lipoprotein complexes by a method used to show antigen-antibody complexes in serum. However, C4 and C2 were not consumed in a serum deficient in C1q. Supplementing this serum with a physiological amount of highly purified C1q resulted in C4 and C2 consumption after addition of the PS, demonstrating that C1q was necessary for the reaction.
ASJC Scopus subject areas
- Molecular Biology