UCT CS Research Document Archive

Conformation and cross-protection in Group B Streptococcus serotype III and Streptococcus pneumoniae serotype 14: a molecular modeling study

Kuttel, Michelle M. and Neil Ravenscroft (2019) Conformation and cross-protection in Group B Streptococcus serotype III and Streptococcus pneumoniae serotype 14: a molecular modeling study. Pharmaceuticals 12(1).

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Abstract

Although the branched capsular polysaccharides of Streptococcus agalactiae serotype III (GBSIII PS) and Streptococcus pneumoniae serotype 14 (Pn14 PS) differ only in the addition of a terminal sialic acid on the GBSIII PS side chains, these very similar polysaccharides are immunogenically distinct. Our simulations of GBSIII PS, Pn14 PS and the unbranched backbone polysaccharide provide a conformational rationale for the different antigenic epitopes identified for these PS.We find that side chains stabilize the proximal bDGlc(1->6)bDGlcNAc backbone linkage, restricting rotation and creating a well-defined conformational epitope at the branch point. This agrees with the glycotope structure recognized by an anti-GBSIII PS functional monoclonal antibody. We find the same dominant solution conformation for GBSIII and Pn14 PS: aside from the branch point, the backbone is very flexible with a “zig-zag” conformational habit, rather than the helix previously proposed for GBSIII PS. This suggests a common strategy for bacterial evasion of the host immune system: a flexible backbone that is less perceptible to the immune system, combined with conformationally-defined branch points presenting human-mimic epitopes. This work demonstrates how small structural features such as side chains can alter the conformation of a polysaccharide by restricting rotation around backbone linkages.

EPrint Type:Journal (On-line/Unpaginated)
Keywords:capsular polysaccharide; carbohydrate antigen; molecular modeling; Group B Streptococcus; Streptococcus pneumoniae; conjugate vaccines
Subjects:J Computer Applications: J.3 LIFE AND MEDICAL SCIENCES
ID Code:1306
Deposited By:Kuttel, Michelle
Deposited On:13 March 2019