title: Salt effects on the conformational stability of the visual G-protein-coupled receptor rhodopsin.
abstract: Membrane protein stability is a key parameter with important physiological and practical implications. Inorganic salts affect protein stability, but the mechanisms of their interactions with membrane proteins are not completely understood. We have undertaken the study of a prototypical G-protein-coupled receptor, the α-helical membrane protein rhodopsin from vertebrate retina, and explored the effects of inorganic salts on the thermal decay properties of both its inactive and photoactivated states. Under high salt concentrations, rhodopsin significantly increased its activation enthalpy change for thermal bleaching, whereas acid denaturation affected the formation of a denatured loose-bundle state for both the active and inactive conformations. This behavior seems to correlate with changes in protonated Schiff-base hydrolysis. However, chromophore regeneration with the 11-cis-retinal chromophore and MetarhodopsinII decay kinetics were slower only in the presence of sodium chloride, suggesting that in this case, the underlying phenomenon may be linked to the activation of rhodopsin and the retinal release processes. Furthermore, the melting temperature, determined by means of circular dichroism and differential scanning calorimetry measurements, was increased in the presence of high salt concentrations. The observed effects on rhodopsin could indicate that salts favor electrostatic interactions in the retinal binding pocket and indirectly favor hydrophobic interactions at the membrane protein receptor core. These effects can be exploited in applications where the stability of membrane proteins in solution is highly desirable.
authors.affiliation: Group of Molecular and Industrial Biotechnology, Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Terrassa, Catalonia, Spain.
authors.forename: Arfaxad
authors.initials: A
authors.lastname: Reyes-Alcaraz
authors.forename: Marlet
authors.initials: M
authors.lastname: Martínez-Archundia
authors.forename: Eva
authors.initials: E
authors.lastname: Ramon
authors.forename: Pere
authors.initials: P
authors.lastname: Garriga
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002152:Calorimetry, Differential Scanning; D002417:Cattle; D002942:Circular Dichroism; D005136:Eye Proteins / Q000737:chemistry* / Q000378:metabolism*; D006868:Hydrolysis / Q000187:drug effects; D007700:Kinetics; D011189:Potassium Chloride / Q000494:pharmacology; D011487:Protein Conformation; D011489:Protein Denaturation / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D012243:Rhodopsin / Q000737:chemistry* / Q000378:metabolism*; D012492:Salts / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology*; D013696:Temperature
chemical_list: D005136:Eye Proteins; D012492:Salts; D000643:Ammonium Chloride; D012965:Sodium Chloride; D011189:Potassium Chloride; D012243:Rhodopsin