title: Structural waters define a functional channel mediating activation of the GPCR, rhodopsin.
abstract: Structural water molecules may act as prosthetic groups indispensable for proper protein function. In the case of allosteric activation of G protein-coupled receptors (GPCRs), water likely imparts structural plasticity required for agonist-induced signal transmission. Inspection of structures of GPCR superfamily members reveals the presence of conserved embedded water molecules likely important to GPCR function. Coupling radiolytic hydroxyl radical labeling with rapid H(2)O(18) solvent mixing, we observed no exchange of these structural waters with bulk solvent in either ground state or for the Meta II or opsin states. However, the radiolysis approach permitted labeling of selected side chain residues within the transmembrane helices and revealed activation-induced changes in local structural constraints likely mediated by dynamics of both water and protein. These results suggest both a possible general mechanism for water-dependent communication in family A GPCRs based on structural conservation, and a strategy for probing membrane protein structure.
authors.affiliation: Department of Pharmacology, Center for Proteomics and Bioinformatics, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4965, USA.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Angel
authors.forename: Sayan
authors.initials: S
authors.lastname: Gupta
authors.forename: Beata
authors.initials: B
authors.lastname: Jastrzebska
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Palczewski
authors.forename: Mark R
authors.initials: MR
authors.lastname: Chance
mesh_terms: D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002853:Chromatography, Liquid; D006868:Hydrolysis / Q000528:radiation effects; D017665:Hydroxyl Radical / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010103:Oxygen Isotopes; D010446:Peptide Fragments / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry*; D012243:Rhodopsin / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D014867:Water / Q000737:chemistry*; D014965:X-Rays
chemical_list: D010103:Oxygen Isotopes; D010446:Peptide Fragments; D043562:Receptors, G-Protein-Coupled; D012997:Solvents; D014867:Water; D017665:Hydroxyl Radical; D012243:Rhodopsin
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