Figure 2.

A: Backbone structure of Il-1β. The four cavities toward the top and bottom of the figure each contain one or two water molecules which are well ordered and hydrogen-bonded by surrounding backbone amides and carbonyl groups. The fifth cavity, located in the center of the molecule, is surrounded by nonpolar side-chains and its occupancy by solvent is contentious. B: Stereo pair with the cyan arrow showing the central apolar cavity in Il-1β [PDB code 2NVH; cf. Fig. 1(B)]. The red arrow at the top shows an internal cavity containing a single water molecule (red); the red arrow at the bottom shows a cavity containing two solvent molecules. The cavities that contain solvent have partial dark-blue and red coloring indicating their polar nature. The view direction is essentially the same as in Figure 2(A) and the two solvent-filled cavities correspond to those at the top left and bottom left in Figure 2(A).