Fig 2. Representation of the two-shell water coordination number (WCN) and the WCN-OH variant.

(A) For a methionine with the side chain exposed to the solvent, the water molecules within 6 Å from the sulfur atom are shown. (B) For a methionine with the side chain only partially exposed to the solvent, water molecules and side chains containing a hydroxyl group are shown. Carbon atoms are colored in cyan, oxygen in red, hydrogen in gray, nitrogen in blue and sulfur in yellow. The sphere represents the 2-solvation shell (radius 6 Å).