Comparison of the structures of ABP and NP2. (a) Ribbon diagram of ABP showing the molecular surface of the central cavity in magenta. The bound tryptamine is shown in blue. The cavity surface was calculated using CASTp (Dundas et al., 2006). (b) Ribbon diagram of NP2 (PDB entry 1euo
; Andersen & Montfort, 2000) showing the molecular surface of the central cavity in magenta. The bound heme is shown in red. (c) Stereoview of the superimposed binding-pocket regions of ABP and NP2. For ABP, C atoms are colored white, O atoms red and N atoms blue. For NP2, C atoms are colored cyan, O atoms red and N atoms blue. Tryptamine of ABP is colored yellow, with its N atoms blue, and heme from NP2 is colored red, with its N atoms blue.