The emerging method of femtosecond crystallography (FX) may extend the diffraction resolution accessible from small radiationsensitive crystals and provides a means to determine catalytically accurate structures of acutely radiation-sensitive metalloenzymes. Automated goniometer-based instrumentation developed for use at the Linac Coherent Light Source enabled efficient and flexible FX experiments to be performed on a variety of sample types. In the case of rod-shaped Cpl hydrogenase crystals, only five crystals and about 30 min of beam time were used to obtain the 125 still diffraction patterns used to produce a 1.6-Å resolution electron density map. For smaller crystals, high-density grids were used to increase sample throughput; 930 myoglobin crystals mounted at random orientation inside 32 grids were exposed, demonstrating the utility of this approach. Screening results from cryocooled crystals of β 2 -adrenoreceptor and an RNA polymerase II complex indicate the potential to extend the diffraction resolution obtainable from very radiation-sensitive samples beyond that possible with undulator-based synchrotron sources.femtosecond diffraction | crystallography | XFEL | structural biology U sing extremely bright, short-timescale X-ray pulses produced by X-ray free-electron lasers (XFELs), femtosecond crystallography (FX) is an emerging method that expands the structural information accessible from very small or very radiation-sensitive macromolecular crystals. Central to this method is the "diffraction before destruction" (1) process in which a still diffraction image is produced by a single X-ray pulse before significant radiation-induced electronic and atomic rearrangements occur within the crystal (1-3). At the Linac Coherent Light Source (LCLS) at SLAC, a single ∼50-fs-long X-ray pulse can expose a crystal to as many X-ray photons as a typical synchrotron beam line produces in about a second. Exposing small crystals to these intense ultrashort pulses circumvents the dose limitations of conventional X-ray diffraction experiments (4) and may produce useful data to resolutions beyond what is achievable at synchrotrons (5). This innovation provides a pathway to obtain atomic information from proteins that only form micrometer-to nanometer-sized crystals, such as many membrane proteins and large multiprotein complexes. Moreover, XFELs enable "diffraction before reduction" data collection to address another major challenge in structural enzymology by providing a means to determine catalytically accurate structures of acutely radiation-sensitive metalloenzyme active sites (6), such as high-valency reaction intermediates that may be significantly photoreduced during a single X-ray exposure at a synchrotron, even at very small doses (7-11). Furthermore, the use of short (tens of femtoseconds) X-ray pulses further complements the structural characterization of biochemical reaction processes by providing access to a time domain two to three orders of magnitude faster (12, 13) than currently accessible using synchrotro...
This paper describes the design, fabrication, and testing of a low-temperature detector mount system which provides thermal isolation between detector electronics, operating at 80 kelvins, and a quartz telescope at 2.5 kelvins. The detector will be used to acquire and track the guide star for the Gravity Probe B Relativity Mission. The detector mount makes use of flex circuit technology for the critical thermal isolator. The detector mounts are configured in a redundant manner through the use of a beamsplitting optic. The entire package mounts to a quartz post through a semi-kinematic mount. Design consideration is given to electromagnetic interference and low-remanent magnetic moment. The detector mounts use a flex cable for electrical connections, as well as thermal grounding. The principal benefit of this design is the ability to operate relatively warm pre-amplifier electronics in a low-temperature environment with minimal disruption to a cryogenic system.Test results have shown this detector mount capable of dissipating less than 2 milliwatts with an 80 K temperature differential.
The concept of hexflash phase analysis described in a previous talk' has been extended to two dimensions. The associated phase unwrapper also works in two dimensions, making the device useful for high speed wave front sensors. A wave front sensor is described which uses high speed 32 x 32 arrays at each focal plane, enabling real time phase measurment at up to 1024 points. These measurements are acquired at a nominal frame rate of 5 KHz. The processing electronics which will be described adds a transport delay of less than 1/20th of a frame. 1.WAVE FRONT SENSINGWave front sensors in use today are usually variations of two fundamental catagories: Hartmann sensors and interferometric measurements. Hartmann sensors, which measure an array of x and y slopes by spot centroiding, are very simple conceptually, and are capable of very high dynamic range measurements. Their disadvantages are that centroiding a large array of spots usually requires very heavy processing capabilities, and /or involves very exotic optical components for optical processing. Alignment of these devices is also very difficult, and can result in a loss of dynamic range. In contrast, the interferometric technique described in this paper involves only relatively common optical components, is easy to align, involves very simple electronic processing, and is easily expandable to any number of channels by selecting the appropriate focal plane. A disadvantage that all interferometric techniques share is the need to perform phase unwrapping.Performing phase unwrapping in 2 dimensions in real time imposes a strong requirement for simplicity and ease of hardware implementation that eliminates many well known robust algorithms from consideration. We demonstrate a solution to this problem in this paper. Finally, the algorithm we will describe is very general -it can be employed with any interferometer (e.g. holographic shearing, Mach -Zender, etc). This paper describes one optical and electronic implementation that is simple and particularly useful. 2.ALGORITHMAn interferometer of any type produces a modulated intensity of the form:
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.