Bacteriophytochromes are photochromic histidine kinases using a biliverdin chromophore.

Phytochromes comprise a principal family of red/far-red light sensors in plants. Although phytochromes were thought originally to be confined to photosynthetic organisms, we have recently detected phytochrome-like proteins in two heterotrophic eubacteria, Deinococcus radiodurans and Pseudomonas aeruginosa. Here we show that these form part of a widespread family of bacteriophytochromes (BphPs) with homology to two-component sensor histidine kinases. Whereas plant phytochromes use phytochromobilin as the chromophore, BphPs assemble with biliverdin, an immediate breakdown product of haem, to generate photochromic kinases that are modulated by red and far-red light. In some cases, a unique haem oxygenase responsible for the synthesis of biliverdin is part of the BphP operon. Co-expression of this oxygenase with a BphP apoprotein and a haem source is sufficient to assemble holo-BphP in vivo. Both their presence in many diverse bacteria and their simplified assembly with biliverdin suggest that BphPs are the progenitors of phytochrome-type photoreceptors.     

Temperature-scan cryocrystallography reveals reaction intermediates in bacteriophytochrome

Light is a fundamental signal that regulates important physiological processes such as development and circadian rhythm in living organisms. Phytochromes form a major family of photoreceptors responsible for red light perception in plants, fungi and bacteria. They undergo reversible photoconversion between red-absorbing (Pr) and far-red-absorbing (Pfr) states, thereby ultimately converting a light signal into a distinct biological signal that mediates subsequent cellular responses. Several structures of microbial phytochromes have been determined in their dark-adapted Pr or Pfr states. However, the structural nature of initial photochemical events has not been characterized by crystallography. Here we report the crystal structures of three intermediates in the photoreaction of Pseudomonas aeruginosa bacteriophytochrome (PaBphP). We used cryotrapping crystallography to capture intermediates, and followed structural changes by scanning the temperature at which the photoreaction proceeded. Light-induced conformational changes in PaBphP originate in ring D of the biliverdin (BV) chromophore, and E-to-Z isomerization about the C(15) = C(16) double bond between rings C and D is the initial photochemical event. As the chromophore relaxes, the twist of the C(15) methine bridge about its two dihedral angles is reversed. Structural changes extend further to rings B and A, and to the surrounding protein regions. These data indicate that absorption of a photon by the Pfr state of PaBphP converts a light signal into a structural signal via twisting and untwisting of the methine bridges in the linear tetrapyrrole within the confined protein cavity.     

Development of the light response in neonatal mammalian rods

The sensitivity to light is low in many neonatal mammals when compared with that in the adult. In human infants at one month of age, for example, the dark-adapted sensitivity for detection of large stimuli is 50 times lower than in the adult, and in rats the overall sensitivity of the neonatal retina is also low compared with the adult. This low sensitivity in the neonate has been attributed to a number of factors, but the possibility that the photoreceptors themselves might be an important limitation on the overall visual sensitivity has not so far been clearly established. Here we record the light response of single neonatal rat rods and find that the sensitivity is considerably lower than in the adult. The response to a single photoisomerization is normal in the neonate, and the sensitivity deficit can therefore be attributed to a low level of functional rhodopsin. Opsin, the protein component of rhodopsin, must be present in normal amounts, as the sensitivity can be restored to adult levels by treating the retina with 9-cis retinal, an active homologue of the native chromophore 11-cis retinal. The low sensitivity of photoreceptors in the neonate can therefore be attributed mainly to a low concentration of 11-cis retinal in the developing retina.     

Functional interaction of phytochrome B and cryptochrome 2

Light is a crucial environmental signal that controls many photomorphogenic and circadian responses in plants. Perception and transduction of light is achieved by at least two principal groups of photoreceptors, phytochromes and cryptochromes. Phytochromes are red/far-red light-absorbing receptors encoded by a gene family of five members (phyA to phyE) in Arabidopsis. Cryptochrome 1 (cry1), cryptochrome 2 (cry2) and phototropin are the blue/ultraviolet-A light receptors that have been characterized in Arabidopsis. Previous studies showed that modulation of many physiological responses in plants is achieved by genetic interactions between different photoreceptors; however, little is known about the nature of these interactions and their roles in the signal transduction pathway. Here we show the genetic interaction that occurs between the Arabidopsis photoreceptors phyB and cry2 in the control of flowering time, hypocotyl elongation and circadian period by the clock. PhyB interacts directly with cry2 as observed in co-immunoprecipitation experiments with transgenic Arabidopsis plants overexpressing cry2. Using fluorescent resonance energy transfer microscopy, we show that phyB and cry2 interact in nuclear speckles that are formed in a light-dependent fashion.     

Woodpile结构中立体空间波导的研究

采用时域有限差分法设计并模拟了微波波段的三维立体结构中任意弯曲波导及空间腔腔耦合波导结构。模拟结果表明,三维立体的woodpile结构除了可以实现平面内任意弯曲波导如C型波导、Z型波导对光的可控制传输外,还可以实现非平面内光的多角度多方向的可控制传输。     

Observations of light-induced structural changes of retinal within rhodopsin

Photo-isomerization of the 11-cis retinal chromophore activates the mammalian light-receptor rhodopsin, a representative member of a major superfamily of transmembrane G-protein-coupled receptor proteins (GPCRs) responsible for many cell signal communication pathways. Although low-resolution (5 A) electron microscopy studies confirm a seven transmembrane helix bundle as a principal structural component of rhodopsin, the structure of the retinal within this helical bundle is not known in detail. Such information is essential for any theoretical or functional understanding of one of the fastest occurring photoactivation processes in nature, as well as the general mechanism behind GPCR activation. Here we determine the three-dimensional structure of 11-cis retinal bound to bovine rhodopsin in the ground state at atomic level using a new high-resolution solid-state NMR method. Significant structural changes are observed in the retinal following activation by light to the photo-activated M(I) state of rhodopsin giving the all-trans isomer of the chromophore. These changes are linked directly to the activation of the receptor, providing an insight into the activation mechanism of this class of receptors at a molecular level.     

Induction of photosensitivity by heterologous expression of melanopsin

Melanopsin has been proposed to be the photopigment of the intrinsically photosensitive retinal ganglion cells (ipRGCs); these photoreceptors of the mammalian eye drive circadian and pupillary adjustments through direct projections to the brain. Their action spectrum (lambda(max) approximately 480 nm) implicates an opsin and melanopsin is the only opsin known to exist in these cells. Melanopsin is required for ipRGC photosensitivity and for behavioural photoresponses that survive disrupted rod and cone function. Heterologously expressed melanopsin apparently binds retinaldehyde and mediates photic activation of G proteins. However, its amino-acid sequence differs from vertebrate photosensory opsins and some have suggested that melanopsin may be a photoisomerase, providing retinoid chromophore to an unidentified opsin. To determine whether melanopsin is a functional sensory photopigment, here we transiently expressed it in HEK293 cells that stably expressed TRPC3 channels. Light triggered a membrane depolarization in these cells and increased intracellular calcium. The light response resembled that of ipRGCs, with almost identical spectral sensitivity (lambda(max) approximately 479 nm). The phototransduction pathway included Gq or a related G protein, phospholipase C and TRPC3 channels. We conclude that mammalian melanopsin is a functional sensory photopigment, that it is the photopigment of ganglion-cell photoreceptors, and that these photoreceptors may use an invertebrate-like phototransduction cascade.     

Light-avoidance-mediating photoreceptors tile the Drosophila larval body wall

Photoreceptors for visual perception, phototaxis or light avoidance are typically clustered in eyes or related structures such as the Bolwig organ of Drosophila larvae. Unexpectedly, we found that the class IV dendritic arborization neurons of Drosophila melanogaster larvae respond to ultraviolet, violet and blue light, and are major mediators of light avoidance, particularly at high intensities. These class IV dendritic arborization neurons, which are present in every body segment, have dendrites tiling the larval body wall nearly completely without redundancy. Dendritic illumination activates class IV dendritic arborization neurons. These novel photoreceptors use phototransduction machinery distinct from other photoreceptors in Drosophila and enable larvae to sense light exposure over their entire bodies and move out of danger.     

植物Annexins研究进展

综述了植物膜联蛋白的结构与功能．植物膜联蛋白具有膜联蛋白家族的基本结构，但其三维结构与动物膜联蛋白有所差异．同动物膜联蛋白一样，植物膜联蛋白可能参与植物细胞的分泌作用、胞吐作用、液泡化过程及低温信号转导过程，也可能具有愈伤葡萄糖合成酶、ATPase／GTPase及过氧化物的活性．植物膜联蛋白可能与果实的成熟有关。     

A rhodopsin is the functional photoreceptor for phototaxis in the unicellular eukaryote Chlamydomonas

Rhodopsin is a visual pigment ubiquitous in multicellular animals. If visual pigments have a common ancient origin, as is believed, then some unicellular organisms might also use a rhodopsin photoreceptor. We show here that the unicellular alga Chlamydomonas does indeed use a rhodopsin photoreceptor. We incorporated analogues of its retinal chromophore into a blind mutant; normal photobehaviour was restored and the colour of maximum sensitivity was shifted in a manner consistent with the nature of the retinal analogue added. The data suggest that 11-cis-retinal is the natural chromophore and that the protein environment of this retinal is similar to that found in bovine rhodopsin, suggesting homology with the rhodopsins of higher organisms. This is the first demonstration of a rhodopsin photoreceptor in an alga or eukaryotic protist and also the first report of behavioural spectral shifts caused by exogenous synthetic retinals in a eukaryote. A survey of the morphology and action spectra of other protists suggests that rhodopsins may be common photoreceptors of chlorophycean, prasinophycean and dinophycean algae. Thus, Chlamydomonas represents a useful new model for studying photoreceptor cells.     

Interaction of glutamic-acid-rich proteins with the cGMP signalling pathway in rod photoreceptors.

The assembly of signalling molecules into macromolecular complexes (transducisomes) provides specificity, sensitivity and speed in intracellular signalling pathways. Rod photoreceptors in the eye contain an unusual set of glutamic-acid-rich proteins (GARPs) of unknown function. GARPs exist as two soluble forms, GARP1 and GARP2, and as a large cytoplasmic domain (GARP' part) of the beta-subunit of the cyclic GMP-gated channel. Here we identify GARPs as multivalent proteins that interact with the key players of cGMP signalling, phosphodiesterase and guanylate cyclase, and with a retina-specific ATP-binding cassette transporter (ABCR), through four, short, repetitive sequences. In electron micrographs, GARPs are restricted to the rim region and incisures of discs in close proximity to the guanylate cyclase and ABCR, whereas the phosphodiesterase is randomly distributed. GARP2, the most abundant splice form, associates more strongly with light-activated than with inactive phosphodiesterase, and GARP2 potently inhibits phosphodiesterase activity. Thus, the GARPs organize a dynamic protein complex near the disc rim that may control cGMP turnover and possibly other light-dependent processes. Because there are no similar GARPs in cones, we propose that GARPs may prevent unnecessary cGMP turnover during daylight, when rods are held in saturation by the relatively high light levels.     

Rhodopsin-like sensitivity of extra-retinal photoreceptors mediating the photoperiodic response in quail

It has been known for some 50 years that birds use photoreceptors in or near the hypothalamus to mediate the photoperiodic responses that control seasonal breeding. So far, however, attempts to identify the photopigment by determining an action spectrum have failed. The problems stem from the selective filtering of light by the tissues surrounding the photoreceptors and the need to deliver defined amounts of light over the days or weeks required to induce a quantitative measure of photostimulation. Here we have developed a technique which produces a quantitative action spectrum for the photoperiodic response in the Japanese quail; the results indicate the presence of a rhodopsin photopigment with a peak sensitivity of approximately 492 nm. The photoreceptors exhibit a level of sensitivity comparable with that of vertebrate visual pigments. We conclude that the brain photoreceptors of birds are based on a rhodopsin/rhodopsin-like photopigment.     

拟南芥铁氧还蛋白基因缺失促进花期提前的初步研究(英文)

拟南芥的红光/远红光受体光敏色素(PHYs)参与花期调节过程,而铁氧还蛋白色素还原酶(FD-BRs)的一种——植物色素合成酶(HY2)对于光敏色素的合成是必不可少的。研究发现拟南芥铁氧还蛋白——AtFd2的基因缺失突变体(Fd2-KO突变体)在长日照与短日照培养条件下,较其野生型而言均表现出花期提前的表型,而且显示AtFd2与AtHY2在叶绿体中发生互作,并且Fd2突变体对光敏色素的反应受到抑制。推测At-Fd2基因的缺失可能通过影响光敏色素介导的相关生理功能进而对植株的花期进行调节。     

Cyclic GMP is involved in the excitation of invertebrate photoreceptors

The hyperpolarizing receptor potential in vertebrate rod photoreceptors appears to be mediated by the second messenger, cyclic GMP. Injection of cGMP into rods or application of cGMP to inside-out membrane patches activates a conductance resembling that produced by light. Light produces a rapid reduction of cGMP in living rods, leading to closure of sodium channels and membrane hyperpolarization. In most invertebrate photoreceptors the response to light is depolarizing. We have investigated whether cGMP is involved in controlling the increase in sodium conductance that underlies this depolarization. We show here that injection of cGMP into Limulus photoreceptors produces a depolarization that mimics the receptor potential. We also show that the cGMP concentration of the squid retina increases rapidly during exposure to light. These results support the hypothesis that cGMP mediates the light-induced depolarization in invertebrate photoreceptors and suggests that vertebrate and invertebrate phototransduction may be more similar than previously thought.     

Isolation of cDNAs Enconding Two Distinct Transcription Factors Binding to DRE cis-acting Element Involved in Cold- and drought-induced Expression of Arabidopsis rd29A Gene

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Photoreceptor excitation and adaptation by inositol 1,4,5-trisphosphate

A central question concerning vision is the identity of the biochemical pathway that underlies phototransduction. The large size of the ventral photoreceptors of Limulus polyphemus renders them a favourite preparation for investigating this problem. The fact that a single photon opens approximately 1,000 ionic channels in these photoreceptors suggests the need for an internal transmitter. We have investigated whether inositol 1,4,5-trisphosphate (InsP3) functions as such an internal transmitter, given that InsP3 may act as an intracellular messenger in other cellular processes. Here we report that in Limulus, intracellular pressure injection of InsP3 both excites and adapts ventral photoreceptors in a manner similar to light.     

Release of endogenous excitatory amino acids from turtle photoreceptors

Responses to light are transmitted from photoreceptors to second-order retinal neurons by chemical synapses that may use an excitatory amino acid (EAA) as the neurotransmitter. This hypothesis is based primarily on the pharmacological actions of EAA agonists and antagonists on the membrane potentials and light responses of second-order neurons. But the release of endogenous EAAs, which is a critical criterion for the identification of EAAs as transmitters, has not been demonstrated. Here we report the use of outside-out membrane patches excised from rat hippocampal neurons to detect the release of EAAs from synaptic terminals of isolated turtle photoreceptors. Electrical stimulation of or application of lanthanum chloride to photoreceptors induced an increase in the frequency of opening of 50-pS channels in the patches. These channels were identified as the class of glutamate-activated channels that are also gated by aspartate and NMDA (N-methyl-D-aspartate). In several photoreceptor-patch pairs, spontaneous channel activity was observed near the synaptic terminals. These results provide strong evidence to support the hypothesis that both rods and cones of the turtle use an EAA as their neurotransmitter.     

woodpile结构中完全带隙的研究

介电常数沿不同方向周期性变化的woodpile结构三维光子晶体存在完全带隙,可以实现立体空间中对光的控制传输。鉴于此,采用时域有限差分方法研究了椭圆截面和长方形截面介质柱形成的光子晶体的完全带隙。结果发现,这两种情况都存在很好的完全带隙,且带隙的宽度受到介质柱不同截面形状的有效调节。     

Modeling of kiwifruit metallothionein kiwi503

Kiwifruit metallothionein, kiwi503, is a typical plant metallothionein protein. It has 63 amino acid residues in two cysteine-rich regions and one spacer region of about 32 residues. In this note, the two cysteine-rich regions and the spacer region have been modeted separatety by the distance geometry and the homology method. The three parts are then connected to generate a three-dimensional structural modet of kiwifruit metallothionein kiwi503. The result shows that there is no structural or energy barrier preventing either cysteine rich domain from independently forming a metal-sulfur chetating cluster. The method can also be applied to predicting the structures of the same type of other proteins. The first two authors contributed equally to this work