Martin Engelhard

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The microbial phototaxis receptor sensory rhodopsin II (NpSRII, also named phoborhodopsin) mediates the photophobic response of the haloarchaeon Natronomonas pharaonis by modulating the swimming behaviour of the bacterium. After excitation by blue-green light NpSRII triggers, by means of a tightly bound transducer protein (NpHtrII), a signal transduction(More)
Microbial rhodopsins, which constitute a family of seven-helix membrane proteins with retinal as a prosthetic group, are distributed throughout the Bacteria, Archaea and Eukaryota. This family of photoactive proteins uses a common structural design for two distinct functions: light-driven ion transport and phototaxis. The sensors activate a signal(More)
A hallmark in prion diseases is the conformational transition of the cellular prion protein (PrP(C)) into a pathogenic conformation, designated scrapie prion protein (PrP(Sc)), which is the essential constituent of infectious prions. Here, we show that epigallocatechin gallate (EGCG) and gallocatechin gallate, the main polyphenols in green tea, induce the(More)
This article describes a method, based on surface-enhanced resonance Raman (SERR) spectroscopy, for studying the reaction dynamics of photoreceptors immobilized on metal electrodes. Time resolution and fresh sample conditions are achieved by synchronizing the rotational and translational motion of a novel kinematic electrode with the duration and time delay(More)
The halobacterial phototaxis receptors sensory rhodopsin I and II (SRI, SRII) enable the bacteria to seek optimal light conditions for ion pumping by bacteriorhodopsin and/or halorhodopsin. The incoming signal is transferred across the plasma membrane by means of receptor-specific transducer proteins that bind tightly to their corresponding photoreceptors.(More)
Bacteriorhodopsin (BR) from Halobacterium salinarum as well as halorhodopsin (pHR) and sensory rhodopsin II (pSRII) from Natronobacterium pharaonis were functionally expressed in E. coli using the method of Shimono et al. IFEBS Lett. (1997) 420, 54-56]. The histidine tagged proteins were purified with yields up to 1.0 mg/l cell culture and characterized by(More)
Archaebacterial photoreceptors mediate phototaxis by regulating cell motility through two-component signalling cascades. Homologs of this sensory pathway occur in all three kingdoms of life, most notably in enteric bacteria in which the chemotaxis has been extensively studied. Recent structural and functional studies on the sensory rhodopsin II/transducer(More)
The photocycle of the photophobic receptor sensory rhodopsin II from N. pharaonis was analyzed by varying measuring wavelengths, temperature, and pH, and by exchanging H2O with D2O. The data can be satisfactorily modeled by eight exponents over the whole range of modified parameters. The kinetic data support a model similar to that of bacteriorhodopsin (BR)(More)
EPR spectroscopy in combination with site directed spin labeling (SDSL) has become a valuable tool for structural investigations as well as for kinetic studies on proteins. This method has been especially useful for membrane proteins in yielding structural and functional data. This information is not easily available from other techniques, like, e.g., X-ray(More)
We present a historical overview of research on microbial rhodopsins ranging from the 1960s to the present date. Bacteriorhodopsin (BR), the first identified microbial rhodopsin, was discovered in the context of cell and membrane biology and shown to be an outward directed proton transporter. In the 1970s, BR had a big impact on membrane structural research(More)