Figure 3. Radial averages of 〈u²〉 and density for bovine serum albumin (BSA, PDB id 4F5S) and insulin degrading enzyme (PDB id 4IOF) in water (TIP3P) at T = 300 K where R is the distance from the protein center of mass.

(a) We see that ρ is relatively high, and correspondingly 〈u²〉 is relatively low, near the center of the relatively large globular protein BSA, a trend that is qualitatively similar to our Ni NP observations in Fig. 2(a) and that epitomizes the arguments of Karplus and coworkers. (b) The example of insulin degrading enzyme reminds us that proteins have special biological functions and structures so that no universal trend between the interior mobility and density of proteins exists. This protein has a binding cavity in its core that accounts for the low density in the center of the protein.