Rhodopsin activation in lipid membranes entails a large influx of bulk water into the protein core. (A) Dark-state rhodopsin has a closed, dehydrated conformation of the 7-transmembrane helical bundle (30). (B) Open metarhodopsin-II conformation is adopted after retinal photoisomerization with outward-tilted TM6 (blue) and extended TM5 (green) helices following pH-dependent breakage of the Glu134–Arg135 salt bridge (31). (C) Large numbers of water molecules (~80–100) enter rhodopsin as determined by osmotic stress data for various-sized polyethylene glycols (PEGs). Smaller PEGs show smaller apparent water influx than more excluded large PEGs. The number of water molecules determined by the universal large osmolyte response is indicated by the dotted line. (D) Increase in virial coefficient ΔC for volume versus osmotic pressure accompanies rhodopsin photoactivation. Larger ΔC is determined in the exclusion limit of larger PEGs with the dotted line as the universal response. (E) Viewed from the intracellular side, dark-state rhodopsin is closed with residues colored by hydrophobicity (red, hydrophobic; white, hydrophilic). (F) The MII state shows an opened hydrophilic cavity (white) to accommodate the influx of bulk water which (G) widens as the C-terminal peptide of the G-protein (here Gi) is docked
💧🧬 Key drug targets in your body, the #GPCRs, need a massive influx of water to activate, even more than their size? Fried et al. found this and more. Dive deeper at doi.org/10.25422/azu... & doi.org/10.1073/pnas.... Image: Fried et al. (2022). CC BY-NC-ND 4.0
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