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Signal Transfer (signal + transfer)
Selected AbstractsSignal Transfer in Haloarchaeal Sensory Rhodopsin, Transducer Complexes,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2008Jun Sasaki Membrane-inserted complexes consisting of two photochemically reactive sensory rhodopsin (SR) subunits flanking a homodimer of a transducing protein subunit (Htr) are used by halophilic archaea for sensing light gradients to modulate their swimming behavior (phototaxis). The SR,Htr complexes extend into the cytoplasm where the Htr subunits bind a his-kinase that controls a phosphorylation system that regulates the flagellar motors. This review focuses on current progress primarily on the mechanism of signal relay within the SRII,HtrII complexes from Natronomonas pharaonis and Halobacterium salinarum. The recent elucidation of a photoactive site steric trigger crucial for signal relay, advances in understanding the role of proton transfer from the chromophore to the protein in SRII activation, and the localization of signal relay to the membrane-embedded portion of the SRII,HtrII interface, are beginning to produce a clear picture of the signal transfer process. The SR,Htr complexes offer unprecedented opportunities to resolve first examples of the chemistry of signal relay between membrane proteins at the atomic level, which would provide a major contribution to the general understanding of dynamic interactions between integral membrane proteins. [source] Heterogeneous distribution of AMPA glutamate receptor subunits at the photoreceptor synapses of rodent retinaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2001Iris Hack Abstract In the retina the segregation of different aspects of visual information starts at the first synapse in signal transfer from the photoreceptors to the second-order neurons, via the neurotransmitter glutamate. We examined the distribution of the four AMPA glutamate receptor subunits GluR1,GluR4 at the photoreceptor synapses in mouse and rat retinae by light and immunoelectron microscopy and serial section reconstructions. On the dendrites of OFF-cone bipolar cells, which make flat, noninvaginating contacts postsynaptic at cone synaptic terminals, the subunits GluR1 and GluR2 were predominantly found. Horizontal cell processes postsynaptic at both rod and cone synaptic terminals preferentially expressed the subunits GluR2, GluR2/3 and GluR4. An intriguing finding was the presence of GluR2/3 and GluR4 subunits on dendrites of putative rod bipolar cells, which are thought to signal through the sign-inverting metabotropic glutamate receptor 6, mGluR6. Furthermore, at the rod terminals, horizontal cell processes and rod bipolar cell dendrites showed labelling for the AMPA receptor subunits at the ribbon synaptic site or perisynaptically at their site of invagination into the rod terminal. The wide distribution of AMPA receptor subunits at the photoreceptor synapses suggests that AMPA receptors play an important role in visual signal transfer from the photoreceptors to their postsynaptic partners. [source] Dynamics Change of Phoborhodopsin and Transducer by Activation: Study Using D75N Mutant of the Receptor by Site-directed Solid-state 13C NMR,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2008Izuru Kawamura Pharaonis phoborhodopsin (ppR or sensory rhodopsin II) is a negative phototaxis receptor of Natronomonas pharaonis, and forms a complex, which transmits the photosignal into cytoplasm, with its cognate transducer (pHtrII). We examined a possible local dynamics change of ppR and its D75N mutant complexed with pHtrII, using solid-state 13C NMR of [3- 13C]Ala- and [1- 13C]Val-labeled preparations. We distinguished Ala C,13C signals of relatively static stem (Ala221) in the C-terminus of the receptors from those of flexible tip (Ala228, 234, 236 and 238), utilizing a mutant with truncated C-terminus. The local fluctuation frequency at the C-terminal tip was appreciably decreased when ppR was bound to pHtrII, while it was increased when D75N, that mimics the signaling state because of disrupted salt bridge between C and G helices prerequisite for the signal transfer, was bound to pHtrII. This signal change may be considered with the larger dissociation constant of the complex between pHtrII and M-state of ppR. At the same time, it turned out that fluctuation frequency of cytoplasmic portion of pHtrII is lowered when ppR is replaced by D75N in the complex with pHtrII. This means that the C-terminal tip partly participates in binding with the linker region of pHtrII in the dark, but this portion might be released at the signaling state leading to mutual association of the two transducers in the cytoplasmic regions within the ppR/pHtrII complex. [source] Influence of a Joining Helix on the BLUF Domain of the YcgF Photoreceptor from Escherichia coliCHEMBIOCHEM, Issue 15 2008Claudia Schroeder Abstract BLUF-domain-comprising photoreceptors sense blue light by utilizing FAD as a chromophore. The ycgF gene product of Escherichia coli is composed of a N-terminal BLUF domain and a C-terminal EAL domain, with the latter postulated to catalyze c-di-GMP hydrolysis. The linkage between these two domains involves a predominantly helical segment. Its role on the function of the YcgF photoreceptor domain was examined by characterizing BLUF domains with and without this segment and reconstituting them with either FAD, FMN or riboflavin. The stability of the light-adapted state of the YcgF BLUF domain depends on the presence of this joining, helical segment and the adenosine diphosphate moiety of FAD. In contrast to other BLUF domains, two-dimensional 1H,15N and one-dimensional 1H NMR spectra of isotope-labeled YcgF-(1,137) revealed large conformational changes during reversion from the light- to the dark-adapted state. Based on these results the function of the joining helix in YcgF during signal transfer and the role of the BLUF domain in regulating c-di-GMP levels is discussed. [source] | ||||||||||