Long-Term Stability of a Vaccine Formulated with the Amphipol-Trapped Major Outer Membrane Protein from Chlamydia trachomatis
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Chlamydia trachomatis is a major bacterial pathogen throughout the world. Although antibiotic therapy can be implemented in the case of early detection, a majority of the infections are asymptomatic, requiring the development of preventive measures. Efforts have focused on the production of a vaccine using the C. trachomatis major outer membrane protein (MOMP). MOMP is purified in its native (n) trimeric form using the zwitterionic detergent Z3–14, but its stability in detergent solutions is limited. Amphipols (APols) are synthetic polymers that can stabilize membrane proteins (MPs) in detergent-free aqueous solutions. Preservation of protein structure and optimization of exposure of the most effective antigenic regions can avoid vaccination with misfolded, poorly protective protein. Previously, we showed that APols maintain nMOMP secondary structure and that nMOMP/APol vaccine formulations elicit better protection than formulations using either recombinant or nMOMP solubilized in Z3–14. To achieve a greater understanding of the structural behavior and stability of nMOMP in APols, we have used several spectroscopic techniques to characterize its secondary structure (circular dichroism), tertiary and quaternary structures (immunochemistry and gel electrophoresis) and aggregation state (light scattering) as a function of temperature and time. We have also recorded NMR spectra of 15N-labeled nMOMP and find that the exposed loops are detectable in APols but not in detergent. Our analyses show that APols protect nMOMP much better than Z3–14 against denaturation due to continuous heating, repeated freeze/thaw cycles, or extended storage at room temperature. These results indicate that APols can help improve MP-based vaccine formulations.
KeywordsAmphipols Vaccine Stability MOMP Chlamydia trachomatis NMR
We thank Stephen White and Wytze van der Veer (UC Irvine) for the use of the circular dichroism spectrophotometers and Fabrice Giusti (IBPC) for the synthesis of amphipol A8–35. We also thank Cambridge Isotopes for the gift of insect cell media for pilot expression studies. This work was supported by grant R01AI092129 from the National Institute of Allergy and Infectious Diseases, by the Centre National de la Recherche Scientifique, by University Paris-7, and by the “Initiative d’Excellence” program from the French State (Grant “DYNAMO”, ANR-11-LABX-0011-01).
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