FIGURE 5.

Formation of a transient proton escape pathway in wt-GFP. Panel A depicts the acidic state A of a wt-GFP from PDB file 1GFL (Yang et al., 1996). Here the Thr-203 switch is “off” and no exit pathway exists. See text for detailed discussion of the HB network. O⋯O distances in angstroms and O–H⋯O angles in degrees. The three shown internal rotations lead to state B′, resembling state B of the S65T mutant in Fig. 2. In particular, χ₁ of Thr-203 was varied from −169° to −50° and for His-148 from −53° to −40°. This establishes a transient proton escape route (blue). Color codes as in Fig. 2, with bb continuation in black. Only Thr-203 and His-148 are rendered with all their atoms (including added hydrogens, not seen in the x-ray structure), the other three amino-acids are represented by selected atoms.