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

    Year: 2018

    Journal: Mol. Pharm., Volume 15, JUL, page 2584–2593

    Authors: Rose, Fabrice; Roovers, Silke; Fano, Mathias; Harloff-Helleberg, Stine; Kirkensgaard, Jacob J. K.; Hejnaes, Kim; Fischer, Per; Foged, Camilla

    Organizations: Innovation Fund Denmark [069-2011-1]; Danish Agency for Science, Technology and Innovation; Danish National Advanced Technology Foundation; Danish Ministry of Science, Technology and Innovation; Drug Research Academy, University of Copenhagen, Denmark; Apotekerfonden of 1991, Denmark; Carlsberg Foundation, Denmark; Lundbeckfonden, Denmark

    Keywords: antigen; biophysics; drug design; protein conformation; protein engineering; protein folding; protein self-assembly; protein stability; Streptococcus; vaccine development

    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 alpha-helix and beta-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 degrees 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 degrees C.
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