title: Involvement of distinct arrestin-1 elements in binding to different functional forms of rhodopsin.
abstract: Solution NMR spectroscopy of labeled arrestin-1 was used to explore its interactions with dark-state phosphorylated rhodopsin (P-Rh), phosphorylated opsin (P-opsin), unphosphorylated light-activated rhodopsin (Rh*), and phosphorylated light-activated rhodopsin (P-Rh*). Distinct sets of arrestin-1 elements were seen to be engaged by Rh* and inactive P-Rh, which induced conformational changes that differed from those triggered by binding of P-Rh*. Although arrestin-1 affinity for Rh* was seen to be low (K(D) > 150 μM), its affinity for P-Rh (K(D) ~80 μM) was comparable to the concentration of active monomeric arrestin-1 in the outer segment, suggesting that P-Rh generated by high-gain phosphorylation is occupied by arrestin-1 under physiological conditions and will not signal upon photo-activation. Arrestin-1 was seen to bind P-Rh* and P-opsin with fairly high affinity (K(D) of~50 and 800 nM, respectively), implying that arrestin-1 dissociation is triggered only upon P-opsin regeneration with 11-cis-retinal, precluding noise generated by opsin activity. Based on their observed affinity for arrestin-1, P-opsin and inactive P-Rh very likely affect the physiological monomer-dimer-tetramer equilibrium of arrestin-1, and should therefore be taken into account when modeling photoreceptor function. The data also suggested that complex formation with either P-Rh* or P-opsin results in a global transition in the conformation of arrestin-1, possibly to a dynamic molten globule-like structure. We hypothesize that this transition contributes to the mechanism that triggers preferential interactions of several signaling proteins with receptor-activated arrestins.
authors.affiliation: Department of Biochemistry, Center for Structural Biology, Institute of Chemical Biology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
authors.forename: Tiandi
authors.initials: T
authors.lastname: Zhuang
authors.forename: Qiuyan
authors.initials: Q
authors.lastname: Chen
authors.forename: Min-Kyu
authors.initials: MK
authors.lastname: Cho
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Vishnivetskiy
authors.forename: Tina M
authors.initials: TM
authors.lastname: Iverson
authors.forename: Vsevolod V
authors.initials: VV
authors.lastname: Gurevich
authors.forename: Charles R
authors.initials: CR
authors.lastname: Sanders
mesh_terms: D019393:Arrestin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry; D016254:Mutagenesis, Insertional; D019906:Nuclear Magnetic Resonance, Biomolecular; D055355:Opsins / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D055668:Photochemical Processes; D011485:Protein Binding; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D019393:Arrestin; D046912:Multiprotein Complexes; D055355:Opsins; D011994:Recombinant Proteins; D012243:Rhodopsin