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Figure 4
Analytical ultracentrifugation of C-DCX. (a) Sedimentation-coefficient distributions c(s) normalized to the total peak area between 0.5 and 4 S. Six sedimentation-velocity experiments were performed at the C-DCX concentrations indicated (micromolar). The higher the concentration, the more prevalent higher-order oligomers are. The concentration-dependent shift of the signal-weighted sedimentation coefficient sw indicates a fast association equilibrium in solution. No aggregation is observed, as none of the species have sedimentation coefficients of >3.5 S. (b) The sedimentation coefficients sw from the data in (a) form an isotherm (black dots). The inset shows the same distribution with a linear scale for the abscissa. Dotted, magenta and black lines represent fits to these data according to the MDT model (reduced χ2 = 4.99 × 105), the isodesmic model (reduced χ2 = 3.07 × 105) and the isodesmic model including corrections for non-ideality (reduced χ2 = 0.8 × 105), respectively. The bottom graph depicts the residuals of the fits to the data. All models deviate <5% from the data. For the isodesmic model the sedimentation coefficient of the dimer was fixed to its theoretical value during the fit, thus limiting oligomer extension to the addition of monomers. For the MDT model, no tetramer formation was allowed by the (improbable) assembly of four monomers into a tetramer and the sedimentation coefficients for the dimer and tetramer were fixed to their theoretical values during the fit.

Journal logoSTRUCTURAL
ISSN: 2059-7983
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