Comparison of the isomerization mechanisms of human melanopsin and invertebrate and vertebrate rhodopsins

Comparative modeling and ab initio multiconfigurational quantum chemistry are combined to investigate the reactivity of the human nonvisual photoreceptor melanopsin. It is found that both the thermal and photochemical isomerization of the melanopsin 11-cis retinal chromophore occur via a space-saving mechanism involving the unidirectional, counterclockwise twisting of the =C11H-C12H= moiety with respect to its Lys340-linked frame as proposed by Warshel for visual pigments [Warshel A (1976) Nature 260(5553):679–683]. A comparison with the mechanisms documented for vertebrate (bovine) and invertebrate (squid) visual photoreceptors shows that such a mechanism is not affected by the diversity of the three chromophore cavities. Despite such invariance, trajectory computations indicate that although all receptors display less than 100 fs excited state dynamics, human melanopsin decays from the excited state ∼40 fs earlier than bovine rhodopsin. Some diversity is also found in the energy barriers controlling thermal isomerization. Human melanopsin features the highest computed barrier which appears to be ∼2.5 kcal mol⁻¹ higher than that of bovine rhodopsin. When assuming the validity of both the reaction speed/quantum yield correlation discussed by Warshel, Mathies and coworkers [Weiss RM, Warshel A (1979) J Am Chem Soc 101:6131–6133; Schoenlein RW, Peteanu LA, Mathies RA, Shank CV (1991) Science 254(5030):412–415] and of a relationship between thermal isomerization rate and thermal activation of the photocycle, melanopsin turns out to be a highly sensitive pigment consistent with the low number of melanopsin-containing cells found in the retina and with the extraretina location of melanopsin in nonmammalian vertebrates.For a long time it was assumed that the human retina contains only two types of photoreceptor cells: the rods and cones responsible for dim-light and daylight vision, respectively. However, recent studies have revealed the existence of a small number of intrinsically photosensitive retinal ganglion cells (ipRGCs) that regulate nonvisual photoresponses (1). ipRGCs express an atypical opsin-like protein named melanopsin (2, 3) which plays a role in the regulation of unconscious visual reflexes and in the synchronization of endogenous physiological responses to the dawn/dusk cycle (circadian rhythms) (4, 5).Melanopsins are unique among vertebrate photoreceptors because their amino acid sequence shares greater similarity to invertebrate than vertebrate rhodopsin (i.e., the photoreceptor of rods) (6, 7). Like rhodopsins, melanopsins feature an up–down bundle architecture of seven transmembrane α-helices incorporating the 11-cis isomer of retinal as a covalently bound protonated Schiff base (PSB11 in Fig. 1A). Light-induced (i.e., photochemical) isomerization of PSB11 to its all-trans isomer (PSBAT) triggers an opsin conformational change that, ultimately, activates the receptor and signaling cascade (8, 9). However, similar to invertebrate and in contrast to vertebrate rhodopsins, melanopsins are bistable (10). Indeed, although vertebrate rhodopsins need a retinoid cycle (11) to regenerate PSB11, melanopsins have an intrinsic light-driven chromophore regeneration function via PSBAT back-isomerization. Furthermore, past studies have shown that melanopsins use an invertebrate-like signal transduction cascade (12).Open in a separate windowFig. 1.PSB11 chromophore reactivity. (A) Chromophore structure and isomerization to PSBAT. (B) Schematic representation of the photochemical (full arrows) and thermal (dashed arrows) isomerization paths. The CI is located energetically above the TS, features a different geometrical structure, and drives a far-from-equilibrium process. ΔE_S1-S0, τ_cis→trans, and Ea^T (in red) are the fundamental quantities computed in the present work.Melanopsins are held responsible for photoentrainment, using the changes of irradiance and spectral composition to adjust the circadian rhythm (13). The different studies carried out so far on melanopsin light sensitivity do not lead to consistent results. Although Do et al. (14) argue that ipRGCs work at extremely low irradiation intensities showing a single-photon response larger than rods, Ferrer et al. (15) conclude that the melanopsin has a reduced sensitivity relative to visual pigments. On the other hand, these photoreceptors would be expected to display high light sensitivity (14). In the vertebrate retina their density is 10⁴ times lower than that of rhodopsins. Moreover, the receptor is not confined in a dedicated cellular domain such as the outer segment of rods and cones, resulting in a ipRGCs photon capture more than 10⁶-fold lower than that of rods and cones per unit of retina illumination. A high sensitivity of melanopsins would also be consistent with their presence in extraretina locations such as in pineal complex, deep brain, and derma of nonmammalian vertebrates (e.g., amphibian) (16–18). The amount of light that can penetrate into such regions is limited and enriched in the red component due to light scattering by the surrounding tissues (14).The molecular-level understanding of the primary light response of melanopsin is a prerequisite for the comprehension of more complex properties such as its activation and sensitivity. Despite numerous studies carried out since its discovery (16), there is presently little information on the molecular mechanism of melanopsin activation. The common PSB11 chromophore of melanopsins and rhodopsins does not guarantee that the same mechanism operates in both photoreceptors. This not only concerns light-induced activation but also thermal activation: a process whose rate limits the photoreceptor light sensitivity and that is currently associated with thermal, rather than photochemical, PSB11 isomerization (19–24).The mechanism of light-induced PSB11 isomerization in vertebrate rhodopsins has been extensively investigated. Spectroscopic studies have shown that in bovine rhodopsin (Rh) the isomerization occurs on a subpicosecond timescale (25–27). Moreover, the observation of ground state (S₀) vibrational coherence (28) is consistent with a direct transfer of the excited state (S₁) population to the photoproduct (Fig. 1B) passing through a conical intersection (CI). Such a path has been located along the S₁ potential energy surface by constructing a multiconfigurational quantum chemistry (MCQC) based computer model of the photoreceptor (29–31) and spectroscopically supported by probing in the infrared (31). More recently (32), the same computer model has been used to map the Rh thermal isomerization path (Fig. 1B) providing information on the transition states controlling the reaction.Here we present a computational study focusing on the mechanism of photochemical and thermal isomerization of human melanopsin (hMeOp). This would require the construction of a computer model of hMeOp starting from the receptor crystal structure. However, the lack of hMeOp crystallographic data does not allow the use of the protocol previously applied in Rh studies. The significant sequence similarity between squid rhodopsin (sqRh), whose crystal structure is available (PDB code: 2Z73) (33), and hMeOp (40%, SI Appendix, Fig. S1) provides the fundamentals for constructing a structural model of hMeOp at a significant atomic resolution. Building on a study by Batista and coworkers (34) on murine melanopsin, we combine comparative modeling of hMeOp with MCQC to construct a quantum mechanics/molecular mechanics (QM/MM) computer model capable of simulating the photochemical and thermal isomerization reactions of hMeOp. The results are then compared with those found using Rh and sqRh models constructed using the same protocol. Such a comparison is expected to provide information on the differences in spectral and functional properties of these evolutionary distant pigments. As we will show below, the models indicate that hMeOp has a faster photochemical isomerization dynamics and a higher thermal isomerization barrier than both Rh and sqRh.     

管状胃和膈肌缝合预防食管癌切除术后胃排空障碍的效果分析

目的总结管状胃和膈肌缝合固定在预防经颈、胸、腹三切15食管癌切除术后胃排空障碍中的应用经验。方法回顾性分析我科2009年6月至2013年7月980例经颈、胸、腹三切口手术治疗食管癌患者,均行管状胃代食管手术。将患者分为两组：A组530例,未作特殊处理,其中食管上段癌63例,食管中段癌382例,食管下段癌85例;B组450例,将胃缝合固定于膈肌,其中食管上段癌43例,食管中段癌343例,食管下段癌64例。比较两组患者术后胃排空障碍的发生情况。结果A组患者均顺利完成手术,无患者死亡。B组与A组相比较,其术后胃排空障碍的发生率显著减少（P〈0．05）。结论在经颈、胸、腹三切口治疗食管癌手术中,通过将管状胃与膈肌缝合固定可以降低经颈、胸、腹三切口食管癌切除术后胃排空障碍的发生率。     

心理干预对胃癌患者心理健康状况的影响

目的探讨心理干预对胃癌患者心理状况的影响。方法对32例胃癌患者进行心理状况调查。根据每个患者的测评结果实施有针对性的心理与行为方式干预措施，比较干预前后患者心理健康状况。结果心理干预前后。除偏执症状外，患者的强迫、人际关系敏感、抑郁、敌对、惊恐、精神病性等维度评分均存在统计学差异（均P〈0．05）。结论心理干预对胃癌患者负性心理状况有明显改善作用。     

Blood bezoar causing obstruction after laparoscopic Roux-en-Y gastric bypass

INTRODUCTION

Bowel obstruction is a known complication after bariatric surgery especially Roux-en-Y gastric bypass. The known etiologies include internal hernia, jejunojejunostomy stricture, ileus, intussusceptions, superior mesenteric artery syndrome, incarcerated port site hernia, and adhesions. Blood bezoar is a rare cause of small intestinal obstruction after Roux-en-Y gastric bypass.

PRESENTATION OF CASE

We are going to present two cases of small bowel obstruction after Roux-en-Y gastric bypass due to blood bezoar.

DISCUSSION

Blood clot as the etiology of small bowel obstruction after Roux-en-Y gastric bypass is an unusual event. In the presence of postoperative small intestinal obstruction an obstructive blood bezoar should be in differential diagnosis. As any other etiology of postoperative obstruction it should be treated immediately to prevent its adverse lethal complications.

CONCLUSION

The best way for prevention of blood bezoar is prevention of bleeding at staple line and doing hemostasis at stapler line.     

Comparison of phosphotungstate and dextran sulfate-Mg2+ precipitation procedures for determination of high density lipoprotein cholesterol

Because of the controversy over the best method for assaying high density lipoprotein (HDL) cholesterol in the clinical laboratory, a commonly used phosphotungstate method for precipitating low density and very low density lipoproteins (LDL and VLDL) was compared with a recently recommended dextran sulfate precipitation method. The accuracy and precision of HDL cholesterol determinations were similar for both methods. Either of these procedures would appear to be equally satisfactory for the assay of HDL cholesterol in the clinical laboratory.     

传染病分子生物学实验教学实践与体会

随着生命科学的快速发展,分子生物学在传染病诊断和治疗研究中的作用日益重要。本文针对传染病专科医院分子生物学实验教学特点,以问题为导向的教学方法（PBL）为核心,从更新教学内容、改进教学方法、丰富教学手段及培养科学思维等方面阐述了研究生细胞生物学实验教学改革的实践及体会。