Anti-complementary properties of polysaccharides isolated from fruit bodies of mushroom Pleurotus ostreatus

A high molecular-weight water-soluble fraction (PO) obtained by the ethanol precipitation of 0.1 N NaOH extracts of the mushroom Pleurotus ostreatus showed 82% anti-complementary activity for complement consumption hemolysis. The PO consisted of 42% carbohydrate (w/w), 50% protein (w/w), and 3% uronic acid (w/w). Fifty-eight percent of the anti-complementary activity decreased by periodate oxidation and 22% by protease digestion, suggesting that the sugar and protein moieties are essential for this activity. Two polysaccharide fractions, PO-IIIa-1 and PO-IIIa-2, with anti-complementary activity were isolated from the PO using DEAE-Sepharose FF followed by Sephadex G75 and Sepharose CL-6B gel permeation chromatographies. The PO- IIIa-2 was found by HPLC to be nearly homogeneous, with the molecular mass of 531 kDa, and showed 96% ITCH₅₀ (inhibition against the total complement hemolysis of deionized water as the control) at a concentration of 1 mg/ml. This fraction contained galactose, mannose, fucose, and glucose with molar ratios of 1.75:1:0.65 and 0.59, respectively. The majority of galactose and mannose units in the PO-IIIa-2 were composed of TGalpl→, →6Galpl→, →2,6Galpl→, and →Manpl→. The PO-IIIa-1 (molecular mass of 2000 kDa), exhibiting higher activity than the PO-IIIa-2, was further purified into two fractions, unbound proteoglycan (PO-IIIa-1A) and bound glucomannan (PO-IIIa- 1B), by affinity chromatography using ConA-Sepharose CL-4B. The anti- complementary activity of each affinity purified fraction decreased as compared to that of the native PO-IIIa-1 fraction, indicating that the formation of complex between both polysaccharide fractions was necessary for full anticomplementary activity.