The lipid terminal of several bacterial polysaccharides have been hypothesized to have a role in anchoring the polysaccharides to the membrane. We have studied the association of isolated membranes from a noncapsular variant of group B Neisseria meningitidis using two polysaccharides possessing very different structures and whose lipid terminals are well characterized, from group C N. meningitidis and Haemophilus influenzae type b. The polysaccharides were treated with Phospholipase A2 or D to remove the fatty acid at the 2 position and the entire lipid terminal respectively. With native group C polysaccharide (both O-acetyl positive and negative), there was about 15% association with isolated membranes which was completely eliminated when the polysaccharide was treated with Phospholipase A2. The native polysaccharide from H. influenzae type b also associated with the isolated membranes from N. meningitidis and the Phospholipase D treated polysaccharide did not. The association of the polysaccharide with the membrane seems to be eliminated whether only a fatty acid is removed or the entire lipid terminal is removed. The binding seems to be due to hydrophobic interactions rather than receptor mediated. We are looking into whether there are more quantitative differences in binding with Phospholipase A2 and D treatments and whether the structures of the polysaccharides are altered in any way.
