Origin of the unique topology of the triangular water cluster in <i>Rubrobacter xylanophilus</i> rhodopsin.

ABSTRACT: The crystal structure of Rubrobacter xylanophilus rhodopsin (RxR) reveals a triangular cluster of three water molecules (W413, W415, and W419) at the extracellular proton-release site, near Glu187 and Glu197. Using a quantum mechanical/molecular mechanical approach, we identified the structural nature of this unique water cluster. The triangular shape is best reproduced when all three water molecules are neutral H₂O with protonated Glu187 and deprotonated Glu197. Attempts to place H₃O⁺ at any of these water molecules result in spontaneous proton transfer to one of the acidic residues and significant distortion from the crystal structure. The plane defined by the triangular water cluster extends into the guanidinium plane of Arg71, with both aligned a

SUBMITTER: Noji T 

PROVIDER: S-EPMC12445927 | biostudies-literature | 2025

REPOSITORIES: biostudies-literature