Temperature-Induced Self-Assembly of the Group B Streptococcus (GBS) Fusion Antigen GBS-NN

• Published in: Molecular pharmaceutics 2018-07, Vol.15 (7), p.2584-2593
• Main Authors: Rose, Fabrice, Roovers, Silke, Fano, Mathias, Harloff-Helleberg, Stine, Kirkensgaard, Jacob J.K, Hejnaes, Kim, Fischer, Per, Foged, Camilla
• Format: Article
• Language: English
• ISSN: 1543-8384; 1543-8392
• DOI: 10.1021/acs.molpharmaceut.8b00101

Group B Streptococcus (GBS) is a leading cause of serious bacterial neonatal infections worldwide, which provides an unmet medical need for a globally effective vaccine. The recombinant GBS fusion antigen GBS-NN contains the N-terminal regions of the GBS Rib and Alpha C proteins. It shows promising immunogenicity eliciting protective immunity in mice and encouraging results in early human clinical trials. Understanding the physical stability of GBS-NN containing conformational B-cell epitopes is crucial to ensure optimal vaccine stability, efficacy, and safety. We initially discovered that GBS-NN is prone to form higher-order structures at elevated temperatures. We therefore investigated the self-assembly behavior of GBS-NN and characterized the higher-order conformational structures as a function of temperature. In the native state, GBS-NN exists as a monomer and has a secondary structure containing α-helix and β-sheet. Langmuir studies demonstrated that the native protein is highly surface-active and forms a monolayer film at the air–water interface because of its amphipathic properties. The conformational stability of GBS-NN was measured as a function of temperature. GBS-NN has an unusual thermal behavior with a phase transition of approximately 61 °C, which is not accompanied by any major changes in the secondary structure. However, the antigen showed irreversible self-assembly as a function of temperature into higher-order structures with a hydrodynamic diameter of approximately 100 nm. Cryo-transmission electron microscopy analyses demonstrated that these self-assemblies consist of vesicular, ring-like structures with a hollow aqueous interior. Therefore, GBS-NN is a physically stable monomeric protein but is prone to temperature-induced self-assembly above 61 °C.