Active water in protein-protein communication within the membrane: the case of SRII-HtrII signal relay.
We detect internal water molecules in a membrane-embedded receptor-transducer complex and demonstrate water structure changes during formation of the signaling state. Time-resolved FTIR spectroscopy reveals stimulus-induced repositioning of one or more structurally active water molecules to a significantly more hydrophobic environment in the signaling state of the sensory rhodopsin II (SRII)-transducer (HtrII) complex. These waters, distinct from bound water molecules within the SRII receptor, appear to be in the middle of the transmembrane interface region near the Tyr199(SRII)-Asn74(HtrII) hydrogen bond. We conclude that water potentially plays an important role in the SRII --> HtrII signal transfer mechanism in the membrane's hydrophobic core.
Archaeal Proteins, Cell Membrane, Halorhodopsins, Hydrophobic and Hydrophilic Interactions, Protein Binding, Protein Interaction Domains and Motifs, Sensory Rhodopsins, Signal Transduction, Spectroscopy, Fourier Transform Infrared, Water