Absorbance Changes by Aromatic Amino Acid Side Chains in Early Rhodopsin Photointermediates

Abstract— Absorbance changes were monitored from 250 to 650 nm during the first microsecond after photolysis of detergent suspensions of bovine rhodopsin at 20°C. Global analysis of the resulting data produced difference spectra for bathorhodopsin, BSI and lumirhodopsin which give the change in absorbance of the aromatic amino acid side chains in these photointermediates relative to rhodopsin. These spectra show that the significant bleaching of absorbance near 280 nm, which has been seen previously for the lumirhodopsin, metarhodopsin I and metarhodopsin II intermediates, extends to times as early as bathorhodopsin. Because no corresponding absorbance increase is observed in the 250-275 nm region, the earliest bleaching of the 280 nm absorbance in rhodopsin is attributed to disruption of a hyperchromic interaction affecting Trp²⁶⁵. Partial decay of this 280 nm bleaching as bathorhodopsin converts to BSI takes place maximally near 290 nm, where Trp²⁶⁵ has been shown to absorb, and could be due to the ring of the retinylidene chromophore resuming a position at the BSI stage that reestablishes the hyperchromic interaction with Trp²⁶⁵. A subsequent change in the 250-300 nm region, which has no counterpart in the visible chromophore bands, indicates the possible presence of a protein-localized process as lumirhodopsin is formed.     

The Octanol/Water Partition Coefficients of Aminimides

Summary. The n-octanol/water partition coefficients of aminimides were measured. The correlation between lgP _ow and the hydration energy obtained as a result of quantum-chemical modelling of a solution is presented.Received March 25, 2003; accepted (revised) May 5, 2003 Published online September 15, 2003     

Influence of Arrestin on the Photodecay of Bovine Rhodopsin

Continued activation of the photocycle of the dim‐light receptor rhodopsin leads to the accumulation of all‐trans‐retinal in the rod outer segments (ROS). This accumulation can damage the photoreceptor cell. For retinal homeostasis, deactivation processes are initiated in which the release of retinal is delayed. One of these processes involves the binding of arrestin to rhodopsin. Here, the interaction of pre‐activated truncated bovine visual arrestin (Arr^Tr) with rhodopsin in 1,2‐diheptanoyl‐sn‐glycero‐3‐phosphocholine (DHPC) micelles is investigated by solution NMR techniques and flash photolysis spectroscopy. Our results show that formation of the rhodopsin–arrestin complex markedly influences partitioning in the decay kinetics of rhodopsin, which involves the simultaneous formation of a meta II and a meta III state from the meta I state. Binding of Arr^Tr leads to an increase in the population of the meta III state and consequently to an approximately twofold slower release of all‐trans‐retinal from rhodopsin.     

Effects of water re-location and cavity trimming on the CASPT2//CASSCF/AMBER excitation energy of Rhodopsin

We have used quantum-mechanics/molecular-mechanics computations based on ab initio multiconfigurational perturbation theory to determine and rationalize the effect of the re-location of one crystallographic water molecule on the vertical excitation energy of the visual pigment rhodopsin. It is found that the re-location of one water molecule to the opposite side of the 11-cis retinal chromophore leads to a large 0.7–0.8 Å contraction in the chromophore—counterion salt-bridge distance. In spite of this structural effect, the change in excitation energy is found to be limited (< 1.5 kcal mol^?1). Through an analysis of different rhodopsin models in terms of “components” (isolated chromophore, isolated chromophore—counterion ion-pair and models deprived of the counterion charges) we show that the limited change of the excitation energy can be related to a displacement of the retinal chromophore to a different spot of the protein cavity.     

Additive Effects of Chlorin E6 and Metal Ion Binding on the Thermal Stability of Rhodopsin In Vitro†

Zinc (Zn²⁺) deficiency causes retinal dysfunctions such as night blindness and neurodegeneration. Because Zn²⁺ binds directly to the photoreceptor rhodopsin and alters its stability, the stabilization of rhodopsin may be key to prevention and treatment of retinal dysfunctions. In this paper, we investigated if not only trace metals but also other nutrients may stabilize rhodopsin structure in vitro. Detailed studies of the thermal stability of secondary and tertiary structure of rhodopsin in the presence and absence of the chlorophyll derivative chlorin e6 alone and together with bivalent metal ions Zn²⁺, Cu²⁺, Fe²⁺, Ni²⁺, Mg²⁺and Mn²⁺ over a temperature range 5–100°C were conducted using circular dichroism and fluorescence spectroscopy. When both chlorin e6 and Zn²⁺ are present, a pronounced increase in the thermal stability of overall secondary structure content is observed compared to either compound alone. This additive capacity is also noted with Cu²⁺, but not when other metal ions and chlorin e6 are combined.     

Steric Hindrance between Chromophore Substituents as the Driving Force of Rhodopsin Photoisomerization: 10-Methyl-13-Demethyl Retinal Containing Rhodopsin

Abstract— A visual chromophore analogue, 10-methyl-13-demethyl (dm) retinal, was synthesized and reconstituted with bleached bovine rhodopsin to form a visual pigment derivative with absorbance maximum at 505 nm. The investigations with this new compound were stimulated from recent results using 13-dm retinal as a chromophore that revealed a remarkable loss in quantum efficiency (φ of 13-dm retinal-containing rhodopsin: 0.30, Ternieden and Gartner, J. Photochem. Photobiol. B Biol. 33, 83–86, 1996). The quantum efficiency of the new pigment was determined as 0.59 by quantitative bleaching using reconstituted rhodopsin as a reference. The very similar quantum efficiencies of rhodopsin and the new pigment give experimental support for the recently presented hypothesis that a steric hindrance between the substituents at positions 10 and 13 in 11- cis -retinal is elevated during the photoisomerization and thus facilitates the rapid photoisomerization of the visual chromophore (Peteanu et al., Proc. Natl. Acad. Sci. USA 90, 11762–11766, 1993). Such steric hindrance is removed from the molecule by the elimination of the methyl group from position 13 and can be re-established via a rearrangement of the substitution pattern by introducing a methyl group at position 10 of 13-dm retinal.     

Sensory Rhodopsin I and Sensory Rhodopsin II Form Trimers of Dimers in Complex with their Cognate Transducers

Archaeal photoreceptors consist of sensory rhodopsins in complex with their cognate transducers. After light excitation, a two‐component signaling chain is activated, which is homologous to the chemotactic signaling cascades in enterobacteria. The latter system has been studied in detail. From structural and functional studies, a picture emerges which includes stable signaling complexes, which assemble to receptor arrays displaying hexagonal structural elements. At this higher order structural level, signal amplification and sensory adaptation occur. Here, we describe electron microscopy data, which show that also the archaeal phototaxis receptors sensory rhodopsin I and II in complex with their cognate transducers can form hexagonal lattices even in the presence of a detergent. This result could be confirmed by molecular dynamics calculations, which revealed similar structural elements. Calculations of the global modes of motion displayed one mode, which resembles the “U”‐”V” transition of the NpSRII:NpHtrII complex, which was previously argued to represent a functionally relevant global conformational change accompanying the activation process [Ishchenko et al. (2013) J. Photochem. Photobiol. B 123, 55‐58]. A model of cooperativity at the transmembrane level is discussed.     

The Light Shall Show the Way-Or: The Conformational Changes of the Retinal Chromophore in Rhodopsin upon Light Activation

No Abstract     

Identification of Two Palmitoyl Groups in Octopus Rhodopsin

Abstract— We determined the structure and site of fatty acid incorporated in octopus rhodopsin using a combination of fluorescence label and enzymatic cleavage methods in conjunction with fast-atom bombardment (FAB) mass spectrometry. A single peptide containing two adjacent cysteines, Cys337 and Cys338, was successfully isolated using the fluorescence from a dye conjugated to Cys345. The FAB mass spectrometric analysis of the peptide (323phe-³⁴⁰phe) revealed that two palmitoyl groups are linked to Cys337 and Cys338 via thioester bonds in octopus rhodopsin as in bovine rhodopsin.     

Octanol/water partition of ionic species, including 544 cations

[structure: see text] Partition coefficients of single ions in the octanol/water system (log P(oct)) have been assigned on the (Ph4As+, Ph4P+) = Ph4B- assumption. The log P(oct) values of Cl-, Br-, and I- ions are then used to obtain the partition coefficients of cations from partition coefficients of the neutral combination of anion and cation. Partition coefficients of 544 cations derived from 585 organic salts from the MedChem database have been studied. The contributions of the aliphatic charge N+ and aromatic charge n+ in these cations have been investigated. The results show that the contributions of N+ and n+ in different homologous series are affected by the attached functional groups and are not constant, although the effect of the central cation is constant along any given homologous series. The latter can be accounted for qualitatively and semiquantitatively by the electrostatic theory of ionic solvation of Abraham and Liszi. A number of regression equations have been established between partition coefficients of ions and partition coefficients of the corresponding neutral species. These equations can be used to estimate octanol/water partition coefficients for additional cations to about 0.5 log unit.     

Light Dynamics of the Retinal-Disease-Relevant G90D Bovine Rhodopsin Mutant

The RHO gene encodes the G-protein-coupled receptor (GPCR) rhodopsin. Numerous mutations associated with impaired visual cycle have been reported; the G90D mutation leads to a constitutively active mutant form of rhodopsin that causes CSNB disease. We report on the structural investigation of the retinal configuration and conformation in the binding pocket in the dark and light-activated state by solution and MAS-NMR spectroscopy. We found two long-lived dark states for the G90D mutant with the 11-cis retinal bound as Schiff base in both populations. The second minor population in the dark state is attributed to a slight shift in conformation of the covalently bound 11-cis retinal caused by the mutation-induced distortion on the salt bridge formation in the binding pocket. Time-resolved UV/Vis spectroscopy was used to monitor the functional dynamics of the G90D mutant rhodopsin for all relevant time scales of the photocycle. The G90D mutant retains its conformational heterogeneity during the photocycle.     

有机溶剂中脂肪酶催化的2—辛醇动力学拆分

利用有机溶剂中假单胞菌脂肪酶催化的对映选择性酯化反应，对外消旋（Ｒ，Ｓ）－２－辛醇进行了光学拆分。分别考察了冻干时酶缓冲液的ｐＨ值和浓度以及２－辛醇酯化的酰基给体（脂肪酸），有机溶剂，反应温度等因素对脂及酶催化性能的影响。结果表明，冻干时酶缓冲液的ｐＨ值和浓度对酶的活力影响很大，而对选择性影响较小。以ｐＨ值为８．３，浓度为２０ｍｍｏｌ／Ｌ的磷酸盐缓冲液最为适合。     

Esterification of Octanoic Acid with Octanol in Microemulsion and Emulsion System

The esterification of octanoic acid with octanol in microemulsion and emulsion system is studied. In the presence of 5–10% dodecylbenzene-sulfonic acid (DBSA), which is a surfactant-type catalyst, high conversion of esterification can be given both in microemulsion and in emulsion system. Compared with emulsion system, single-phase microemulsion is a more effective reaction system for esterification, with the advantages of comparatively little influence by the amount of water, no need of hard stirring, and stable state when laid long. The esterification of other fatty acids and alcohols in this reaction system were also accomplished in favorable conversion.     

固相微萃取技术在估算多环芳烃的辛醇-水分配系数中的应用

采用固相微萃取 气相色谱／质谱联用技术分析了水中１１种多环芳烃,并获得其平衡时的分配系数。当固相微萃取纤维上涂渍的固定液被视为一种有机溶剂时,根据萃取系统间线性的自由能关系,建立了聚二甲基硅氧烷 水分配系数（Ｋｓｗ）与正辛醇 水分配系数（Ｋｏｗ）间的关系式,并将其应用于估算其它多环芳烃的未知的醇 水分配系数。所建立的方法简单、快速,与Ｌｅｏ碎片法相比,可以更精确地估算取代基位置不同的同分异构体的Ｋｏｗ。     

QSPR Study on Octanol/water Partition Coefficient （lgKow） of Substituted Naphthalin Compounds

Structural parameters of 24 substituted naphthalin compounds were computed at four levels using Hartree-Fock and DFT methods. Based on the experimental data of octanol/water partition coefficient (lgKow),three-parameter (energy of the highest occupied molecular orbital (EHOMO),the most positive atomic net charges of molecule (q+) and molecular average polari-zability (α)) dependent equations were developed using structural parameters as theoretical des-criptors. Especially,lgKow dependent equation calculated at the HF/6-311G** level is more advantageous than others in view of their correlation and predictive abilities. This dependent equation was validated by variance inflation factors (VIF) and t-test methods and used to predict lgKow of eight designed compounds. Upon comparison,the predictive abilities of our work are all more advantageous than those calculated from molecular property calculator program.     

Identification of a Single Phosphorylation Site Within Octopus Rhodopsin

Abstract— Light-dependent phosphorylation of rhodopsin (Rho) is a first step in the desensitization of the signaling state of the receptor during vertebrate and invertebrate visual transduction. We found that only ³⁵⁸Ser of the photoac-tivated octopus Rho (oRho*) was phosphorylated by octopus rhodopsin kinase (oRK). Tryptic truncation of the C-terminal PPQGY repeats of oRho that follow the phosphorylation region did not influence spectral or G-protein activation properties of oRho but abolished phos phorylation. Despite significant structural differences between oRK and mammalian RK, these results provide i further evidence of the importance of singly phosphorylated species of Rho* in the generation of arrestin binding sites.     

Rhodopsin deactivation is affected by mutations of Tyrl91

The 9-methyl group of 11-cis retinal is important in the efficient formation of the active conformation of rhodopsin, Meta II. Here, Tyrl91 rhodopsin mutants were generated because of its proximity to that methyl group in the dark structure. If photoactivation results in movement of the 9-methyl group toward Tyrl91, the steric interactions involved with activation and/or deactivation might not be as tightly coupled in mutant proteins with smaller amino acids at that position. Tyrl91 mutations have no effect on the dark pigment. However, after photobleaching, the lifetime of Meta II is shorter; Meta II decays quickly into two inactive species: (1) a Meta III or Meta III-like species and (2) opsin and free retinal. The Meta III-like fraction maintains the covalent Schiff base linkage of the chromophore much longer than the wild type. On the other hand, the fast chromophore release is similar to cone pigments. Taken together, the data suggest that the role of the 9-methyl group after photo-isomerization is not only to form Meta II efficiently, but also to maintain its active conformation and allow for the timely hydrolysis of the Schiff base. Perturbation of this interaction effects changes in the hydrolysis of the Schiff base and for the case of the Y191A mutation the folded structure of the protein after photobleaching.     

Effect of opsin on the shape of the potential energy surfaces at the conical intersection of the Rhodopsin chromophore

In order to disentangle the role of the protein in the control of the photoisomerization of the chromophore of the visual pigment Rhodopsin, we compare the structure of the ground and excited potential energy surfaces of gas-phase and opsin-embedded 11-cis retinal chromophore at the corresponding (lowest energy) conical intersections. It is shown that, along the branching plane, the asymmetric opsin environment destabilizes one of the ground state relaxation channels emerging from the conical intersection. This suggests that opsin promotes the formation of the product (bathorhodopsin) via enhanced decay probability along the all-trans exit channel. In contrast, in the gas-phase no significant structural difference has been found for the channels that lead towards the 11-cis or all-trans forms of the chromophore.