INTERACTION OF THE C-POLYSACCHARIDE OF STREPTOCOCCUS-PNEUMONIAE WITH THE RECEPTOR ASIALO-GM1

C-polysaccharide (PnC) is the major surface component of pneumococci c ontaining phosphoryl choline residues. In order to investigate the pos sibility that PnC can bind to glycolipid receptors present on epitheli al cells we extracted carbohydrate material from a nonencapsulated str ain of pneumococci. The components of the extract were separated by ge l permeation chromatography. An ELISA was used for detection of fracti ons binding to the pneumococcal glycolipid receptor asialo-GM1. These fractions were pooled and analysed by nuclear magnetic resonance spect roscopy (NMR). The H-1 NMR spectrum showed good agreement with a refer ence spectrum of pure PnC showing that this substance was the major co mponent. Binding of the purified PnC to asialo-GM1 was unaffected by p rotease K treatment. Immunoblots of the purified PnC after separation by SDS-PAGE resulted in a characteristic banding pattern. PnC could be released from pneumococci by heat treatment of whole bacteria in buff er as shown by reaction with a monoclonal antibody specific for the ph osphoryl choline determinant. After separation by SDS-PAGE of the comp onents of the heat extract, immunoblots showed the presence of bands c haracteristic for PnC. Eluates from the characteristic bands in the ge l were shown to contain material binding to asialo-GM1. This binding w as not reduced upon treatment with protease K. Pneumococci deprived of choline by cultivation in a medium containing ethanolamine as the onl y amino alcohol source did not bind to asialo-GM1, indicating that the phosphoryl choline residue of PnC is essential for the interaction be tween PnC and the glycolipid receptor. These data provide evidence tha t PnC containing an intact phosphoryl choline residue is a ligand resp onsible for binding of pneumococci to the receptor asialo-GM1. (C) 199 6 Academic Press Limited.