MOLECULAR RECOGNITION OF ANTIGENIC POLYSACCHARIDES - A CONFORMATIONALCOMPARISON OF CAPSULES FROM STREPTOCOCCUS-PNEUMONIAE SEROGROUP-9

Aqueous solution conformations of three antigenic bacterial capsular p olysaccharides (CPS) from S. pneumoniae serogroup 9 were determined us ing a combination of NMR data (NOE build-up rates and conformation-dep endent chemical shifts), simulated annealing, and molecular dynamics s imulations. Each polymer adopts a flexible extended ribbon conformatio n in solution. Conformations of structural elements shared by each PS are indistinguishable. Differences in conformations are minor and loca lised at the sites of structural variations; there is no evidence of l ong-range stabilisation of a secondary structure. It is likely that an tigenic specificity of Group 9 PS is dominated by local structural var iation rather than by conformational differences.