Table 2. Biophysical data for GFP solutions at low sucrose or high trehalose-high histidine conditions.

Estimates of the intrinsic viscosity [η] and effective crowding factor (k/ν) for high cosolute were extracted from the Ross-Minton equation fits of data in Figure 1. The error in the intrinsic viscosity and effective crowding factor k/ν is the error in the nonlinear fit to Equation 1, while the error in the zeta potential represents the standard deviation from twelve measurements with 70 runs determining the zeta potential for each measurement for two individual samples for each variant at low sucrose or high trehalose-high histidine conditions. For comparison, the theoretical intrinsic viscosity and effective crowding factor of a hydrated hard particle with the same aspect ratio as sfGFP is shown.

sfGFP variant	Solvent viscosity (cP)	Intrinsic viscosity (ml/g)	k/ν	Zeta potential in low sucrose-low histidine conditions, 1 mg/ml protein (mV)	Zeta potential in high trehalose-high histidine conditions, 1 mg/ml protein (mV)	Calculated isoelectric point	Measured melting temperature (°C)
−18	2.58 ± 0.03	5.3 ± 0.5	0.5 ± 0.1	−7.7 ± 0.9	0.1 ± 1.2	5.1	93.0
sfGFP	2.58 ± 0.03	4.9 ± 0.6	0.6 ± 0.1	−1.2 ± 0.1	−0.8 ± 2.1	6.4	92.4
+15	2.58 ± 0.03	5.1 ± 1.4	0.6 ± 0.2	7 ± 2	1.4 ± 1.6	10.5	89.2
Hard particle (L/D =1.8)	2.58	5.5	0.5	n/a	n/a	n/a	n/a