Fig. 6.

The apparent viscosity in A2780 human cells and in E. coli. A. The apparent viscosity, η^app, shows a positive dependence on protein net charge, with increasing η^app for positive protein surfaces. Colour codes are as in Fig. 1 and the dashed line is an exponential fit to the data points to guide the eye. The offset corresponds to water viscosity at infinite repulsion, while the exponentiality is adopted from the apparent exponential behaviour of the E. coli data. B. The same data as in the left panel compared to E. coli data (squares), N.B. the different axis scales. The large squares correspond to η^app in E. coli for the three probe proteins, and the smaller faded squares to surface mutations, as determined from their in-cell NMR 1D-HMQC intensity. The blue triangle represents the apparent viscosity of TTHA^pwt in E. coli determined by the NMR relaxation rate R₂, showing that the two methods are equivalent. Orange markers show the apparent viscosity for HAH1^K57E. C. The observed η^app in the two organisms correlate. The slope, however, is far from unity, indicating that the change in η^app upon surface-charge mutation is 6 times stronger in E. coli.