Figure 1.

 Schematic representation of the reference state. (A) An illustration showing why only a fraction of a spherical shell generally contributes to the normalization function (Equation 3). (B) A pair of noninteracting atoms in a protein is modeled by two points positioned randomly inside a sphere with radius a; the points are at distance r from each other. The normalization function n(r) in Equation 7 corresponds to repeating this random assignment for an infinite number of times. (C) The definition of terms used to write Equations 8–11. The large and small spheres are the reference and probe spheres, respectively.