Functional Water Dynamics in Rhodopsin Using Solid‐State Deuterium NMR Spectroscopy

Abstract

G‐protein‐coupled receptors (GPCRs) are the largest family of cell membrane‐bound proteins that detect extracellular stimuli and transduce signals to activate intracellular functions. Drugs that target GPCRs also account for about 27% of the global market share of therapeutic drugs, with aggregated sales for 2011–2015 of ca. US $890 billion [1]. Hydration is essential for protein tertiary folding and activity, and therefore knowledge of hydration water dynamics is vital for understanding the GPCR activation mechanism [2]. We studied rhodopsin hydration as a prototype for GPCRs, where the role of water in the rhodopsin activation mechanism has been recently explored using quasi‐elastic neutron scattering (QENS) methods [3]. We developed methods for generating powdered samples, notable for exceptionally high protein content while retaining photochemical functionality. The powdered GPCR samples are suitable for biophysical experiments to study the dynamic process of rhodopsin activation [4], where the protein is hydrated using vapor phase absorption in a controlled manner. We propose that the internal protein dynamics (β‐fluctuations) are coupled to the solvent shell, while large‐scale protein domain motions (α‐fluctuations) are coupled to the bulk solvent. To test our hypothesis of functional water interactions, we studied rhodopsin hydration shell dynamics using solid‐state 2H NMR spectroscopy at various hydration levels and temperatures [5]. From the spectral features at 200 K, we identified two dynamically distinguishable protein hydration regions. The broad quadrupolar splitting at approximately 180 kHz is due to bulk water; however, the anisotropic narrow component is a result of water molecules dynamically perturbed by rhodopsin. Additional solid‐state 2H NMR relaxation investigations of molecular dynamics of the rhodopsin‐bound water shell are in progress. Our future focus is on a comparative study of water dynamics in the light activated state and the dark state of the visual photoreceptor.Support or Funding InformationThis work was supported by the NIH (EY026041 and EY012049) and the NSF (MCB 1817862).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.