Figure 1. Solution viscosity increases exponentially with sfGFP protein concentration under low cosolute and high cosolute conditions.

The solution viscosity was measured for each of three sfGFP variants at different protein concentrations in the two formulations. A, Under low cosolute conditions in low sucrose buffer (10 mM histidine, 146 mM sucrose, pH 5.8), only the +15 variant remained soluble, with moderate viscosities at concentrations >200 mg/ml. B, Under high cosolute conditions in histidine-high trehalose buffer (~320 mM histidine, ~660 mM trehalose and pH 5.8), all three sfGFP variants remained soluble, with moderate viscosities up to 250 mg/ml. Data for each protein variant was collected from at least two separate experiments with at least two different protein preparations. Error bars represent the range of replicate measurements; data points shown for each variant come from at least two independent formulations with two different protein preparations. The experimental data were fit to Ross and Minton’s modified Mooney viscosity model with the model fits shown as solid lines of the same color as the corresponding icons. The solid black line represents the theoretical Ross-Minton viscosity profile for a hard particle of the same aspect ratio sfGFP (see text for details).