Figure 1: Effects of macromolecular crowding.

(a) Random walk in a crowded environment. Simulation for random walk (red) of a 30 kDa protein in the presence (upper panel) or absence (bottom panel) of 18,000 ribosomes as crowding agents in a volume of an E. coli cell. The simulation was based on the calculation of diffusion coefficient using the D=(k_BT)/3 πηd where k_BT is scaling factor of Boltzmann constant and the temperature, η is a viscosity value for the interior of an E. coli cell=3.5 × 10⁻³ Kg m⁻¹ s⁻¹ (ref. 48), d is the diameter of the particle used in the simulation=30 Å. The average displacement was computed as follows: A=2*R*D*τ, where τ is the interval for displacement=0.0001, s and R is the dimensions=3. (b) Calculation of the volume that PEG of different sizes (1, 4 and 8 kDa) occupies at different concentrations. At 4% (40 mg ml⁻¹), PEG 1 kDa occupies 8% of the volume in a test tube; 4% PEG 1 kDa provides the approximate crowding effect found in vivo (ref. 47). (c) Translational diffusion of 1 mM lysozyme in the presence or the absence of 4% PEG 1 kDa determined using DOSY-NMR. The logarithm of the relative intensity is plotted against the square of the gradient strength ranging from 15 to 80 G cm⁻¹. The decrease in magnetization with increasing gradient strength was analysed using the equation: where D is the diffusion coefficient with k_B is the Boltzmann constant, T the temperature, η the viscosity, F the dimensionless Perrin factor, r_S the hydrodynamic radius of the molecule q=γδg, Δ=150 ms (separation of the gradient echo), δ=2.5 ms (gradient duration), γ the gyromagnetic ratio of the nucleus and g the strength of the gradient (ranging from 15 to 80 G cm⁻¹. Thirty two points were recorded in the indirect dimension. DMSO was used as an internal reference.