An asymmetric and slightly dimerized structure for the tetanus toxoid protein used in glycoconjugate vaccines

► Tetanus toxoid important conjugation for carbohydrate vaccines. ► Physical nature in solution needs elucidating. ► Sedimentation velocity shows small (∼14%) dimerization. ► Dimers not in reversible equilibrium. ► Overall asymmetric conformation. Tetanus toxoid protein has been characterized with regard oligomeric state and hydrodynamic (low-resolution) shape, important parameters with regard its use in glycoconjugate vaccines. From sedimentation velocity and sedimentation equilibrium analysis in the analytical ultracentrifuge tetanus toxoid protein is shown to be mostly monomeric in solution (∼86%) with approximately 14% dimer. The relative proportions do not appear to change significantly with concentration, suggesting the two components are not in reversible equilibrium. Hydrodynamic solution conformation studies based on high precision viscometry, combined with sedimentation data show the protein to be slightly extended conformation in solution with an aspect ratio ∼3. The asymmetric structure presents a greater surface area for conjugation with polysaccharide than a more globular structure, underpinning its popular choice as a conjugation protein for glycoconjugate vaccines.