Fig. 10

Cleft-like channels filled with water (oxygen) molecules in the β-barrel frame between β7 and β10 sheets of DronPa (a) (Reproduced from [106] with the permission of Portland Press Ltd.), TurboGFP (b) (Reproduced from [107] with the permission of John Wiley and Sons), mCherry (c) (Reproduced from [95] with the permission of AIP Publishing LLC.), and KillerOrange/mKillerOrange (d) (Figure from [108] and Creative Commons license). a DronPa: The cleft (indicated by the broken line) near to strand β7 is conserved. The red double headed arrow indicates the width of the cleft. Water molecules are shown as the cyan spheres, building hydrogen-bonded connection between the chromophore and the aqueous environment. The protein region around the opening and the chromophore is shown as the ball-and-stick model. b TurboGFP: A pore leading to the TurboGFP chromophore. The chromophore is highlighted in green and Val 197 in red. The protein surface (gray) is cut to show the pore and the chromophore cavity. The sections of secondary structure elements are shown as the yellow cartoons. Relevant water molecules are depicted as the magenta spheres. c mCherry: The superposition of ribbon structures of red (mCherry) and yellow (citrine) fluorescent proteins. The β7–β10 region is displayed with a space filling model to show that the gap in mCherry is larger than that in citrine. d KillerOrange (dimer) and mKillerOrange (monomer): The pore is filled by four water molecules connecting the indole moiety of the chromophore with the protein exterior. The water channel (residues shown in yellow) with a chain of seven water molecules (red spheres) and the pore (residues shown in blue) filled with four water molecules. The residues mutated in this work are labeled in red