Search results for "opsins"
showing 10 items of 26 documents
Key roles for freshwater A ctinobacteria revealed by deep metagenomic sequencing
2014
Freshwater ecosystems are critical but fragile environments directly affecting society and its welfare. However, our understanding of genuinely freshwater microbial communities, constrained by our capacity to manipulate its prokaryotic participants in axenic cultures, remains very rudimentary. Even the most abundant components, freshwater Actinobacteria, remain largely unknown. Here, applying deep metagenomic sequencing to the microbial community of a freshwater reservoir, we were able to circumvent this traditional bottleneck and reconstruct de novo seven distinct streamlined actinobacterial genomes. These genomes represent three new groups of photoheterotrophic, planktonic Actinobacteria.…
Interfacial water structure controls protein conformation.
2007
A phenomenological theory of salt-induced Hofmeister phenomena is presented, based on a relation between protein solubility in salt solutions and protein-water interfacial tension. As a generalization of previous treatments, it implies that both kosmotropic salting out and chaotropic salting in are manifested via salt-induced changes of the hydrophobic/hydrophilic properties of protein-water interfaces. The theory is applied to describe the salt-dependent free energy profiles of proteins as a function of their water-exposed surface area. On this basis, three classes of protein conformations have been distinguished, and their existence experimentally demonstrated using the examples of bacter…
The effect of water on protein dynamics
2004
Neutron diffraction and spectroscopy were applied to describe the hydration and dynamics of a soluble protein and a natural membrane from extreme halophilic Archaea. The quantitative dependence of protein motions on water activity was clearly illustrated, and it was established that a minimum hydration shell is required for the systems to access their functional resilience, i.e. a dynamics state that allows biological activity.
Probing a Polar Cluster in the Retinal Binding Pocket of Bacteriorhodopsin by a Chemical Design Approach
2012
Bacteriorhodopsin has a polar cluster of amino acids surrounding the retinal molecule, which is responsible for light harvesting to fuel proton pumping. From our previous studies, we have shown that threonine 90 is the pivotal amino acid in this polar cluster, both functionally and structurally. In an attempt to perform a phenotype rescue, we have chemically designed a retinal analogue molecule to compensate the drastic effects of the T90A mutation in bacteriorhodopsin. This analogue substitutes the methyl group at position C(13) of the retinal hydrocarbon chain by and ethyl group (20-methyl retinal). We have analyzed the effect of reconstituting the wild-type and the T90A mutant apoprotein…
Coreconstitution of bacterial ATP synthase with monomeric bacteriorhodopsin into liposomes. A comparison between the efficiency of monomeric bacterio…
1987
The conditions for coreconstitution of a bacterial ATP synthase and bacteriorhodopsin into lecithin liposomes and for light driven ATP synthesis have been optimized. A rate of maximally 280 nmol ATP min-1 mg ATP synthase-1 was achieved with monomerized bacteriorhodopsin compared with a rate of up to 45 nmol ATP min-1 mg-1 found for proteoliposomes containing bacteriorhodopsin in the form of purple membrane patches. The different rates are explained by the finding that monomeric bacteriorhodopsin is more homogeneously distributed among the liposomes than the purple membrane patches. The final activities depended on both the purification method for the two proteins and the coreconstitution pr…
Convergence of Cortical and Sensory Driver Inputs on Single Thalamocortical Cells
2013
Ascending and descending information is relayed through the thalamus via strong, "driver" pathways. According to our current knowledge, different driver pathways are organized in parallel streams and do not interact at the thalamic level. Using an electron microscopic approach combined with optogenetics and in vivo physiology, we examined whether driver inputs arising from different sources can interact at single thalamocortical cells in the rodent somatosensory thalamus (nucleus posterior, POm). Both the anatomical and the physiological data demonstrated that ascending driver inputs from the brainstem and descending driver inputs from cortical layer 5 pyramidal neurons converge and interac…
Circadian gene expression patterns of melanopsin and pinopsin in the chick pineal gland
2004
The directly light-sensitive chick pineal gland contains at least two photopigments. Pinopsin seems to mediate the acute inhibitory effect of light on melatonin synthesis, whereas melanopsin may act by phase-shifting the intrapineal circadian clock. In the present study we have investigated, by means of quantitative RT-PCR, the daily rhythm of photopigment gene expression as monitored by mRNA levels. Under a 12-h light/12-h dark cycle, the mRNA levels of both pigments were 5-fold higher in the transitional phase from light to dark than at night, both in vivo and in vitro. Under constant darkness in vivo and in vitro, the peak of pinopsin mRNA levels was attenuated, whereas that of melanopsi…
Changes in the hydrogen-bonding strength of internal water molecules and cysteine residues in the conductive state of channelrhodopsin-1
2014
Water plays an essential role in the structure and function of proteins, particularly in the less understood class of membrane proteins. As the first of its kind, channelrhodopsin is a light-gated cation channel and paved the way for the new and vibrant field of optogenetics, where nerve cells are activated by light. Still, the molecular mechanism of channelrhodopsin is not understood. Here, we applied time-resolved FT-IR difference spectroscopy to channelrhodopsin-1 from Chlamydomonas augustae. It is shown that the (conductive) P2(380) intermediate decays with τ ≈ 40 ms and 200 ms after pulsed excitation. The vibrational changes between the closed and the conductive states were analyzed in…
Crystal structures of bR(D85S) favor a model of bacteriorhodopsin as a hydroxyl-ion pump
2003
AbstractStructural features on the extracellular side of the D85S mutant of bacteriorhodopsin (bR) suggest that wild-type bR could be a hydroxyl-ion pump. A position between the protonated Schiff base and residue 85 serves as an anion-binding site in the mutant protein, and hydroxyl ions should have access to this site during the O-intermediate of the wild-type bR photocycle. The guanidinium group of R82 is proposed (1) to serve as a shuttle that eliminates the Born energy penalty for entry of an anion into this binding pocket, and conversely, (2) to block the exit of a proton or a related proton carrier.
Computational evidence in favor of a two-state, two-mode model of the retinal chromophore photoisomerization
2000
In this paper we use ab initio multiconfigurational second-order perturbation theory to establish the intrinsic photoisomerization path model of retinal chromophores. This is accomplished by computing the ground state ( S 0 ) and the first two singlet excited-state ( S 1 , S 2 ) energies along the rigorously determined photoisomerization coordinate of the rhodopsin chromophore model 4- cis -γ-methylnona-2,4,6,8-tetraeniminium cation and the bacteriorhodopsin chromophore model all- trans -hepta-2,4,6-trieniminium cation in isolated conditions. The computed S 2 and S 1 energy profiles do not show any avoided crossing feature along the S 1 reaction path and maintain an energy gap >20 kcal⋅…