MACCHESS PROGRAM FOR MICROCRYSTALLOGRAPHY

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Microcrystallography at MacCHESS greatly extends the capability of the stations and significantly increases the success of MacCHESS users with difficult samples, as has been illustrated in the accomplishments,Section C. In the coming project period, we will work closely with key collaborators to further develop microcrystal methodology to facilitate the structural analysis of challenging biological systems such as: 1) complex aggregates such as those that make up the amyloid fibrils associated with Alzheimer's disease (Eisenberg, UCLA) [102], 2) membrane proteins grown in lipidic mesophases, particularly those associated with Pseudomonas aeruginosa, an opportunistic pathogen responsible for many hospital-acquired infections (Caffrey, Univ. of Limerick, Ireland and Ohio State Univ.), 3) the gating properties and conformational transitions necessary for ion channel function (MacKinnon, Rockefeller Univ.) and biomedically important G protein-coupled receptors (Navarro, U. Texas Medical Branch). Below is a brief summary of the challenges confronted by these collaborators that motivate the microcrystal technical program. More information about the collaborators' work is given in section D.2.2. A number of important human diseases involve the harmful aggregation of proteins. Best known are Alzheimer`s disease, transmissible spongiform encephalopathies, and Type II diabetes mellitus. The Eisenberg group has managed to produce microcrystals of key amyloid-forming peptides, in spite of their tendency to form fibers rather than regular crystal lattices. These ultra-small needles, typically 1 micron in the narrow diameter, require special harvesting and mounting techniques. To date, usable diffraction data have only been obtainable using the microcrystallography beamline at the ESRF in Grenoble, France, a facility that is not often available to US researchers. These fibril crystals strain the limits of optical light microscopy used for positioning at beamlines. They are a unique example of sample dry mounting and their smallness serves as an important benchmark for mechanical precision of sample positioning. The smallness of X-ray illuminated volume combines with the relative durability of the crystals and their small unit cell to produce an excellent test case for the proposed micro CCD detectors (described below). Fibrils also exhibit highly variable quality, making it necessary to screen multiple samples to obtain optimal data. The challenging membrane protein crystals grown by the MacKinnon group are also often small (< 20 microns) and tend to be variable in their diffraction quality. The variability can sometimes mean that a few percent of the crystals are suitable for data collection. For this reason, Dr. MacKinnon had encouraged us to develop methods to optimize data collection on small crystals and to implement robotics to rapidly screen large numbers to identify useful crystals. Membrane associated protein crystals grown by the Caffrey and Navarro groups pose additional challenges. Beyond the fact that they are small, fragile, and of significant unit cell size, the unusual matrices in which the crystals are grown (such as cubic lipidic mesophases), present unique visualization and harvesting challenges. The use of more sophisticated visualization methods, such as confocal microscopy, should prove valuable in this case. We propose to explore how a combination of microbeams, sample manipulation and advanced visualization methods can be used to identify good quality regions on otherwise defective crystals. In this regard, Cornell is home to one of the world centers for multiphoton confocal microscopy. The Developmental Resource for Biophysical Imaging Opto-Electronics (DRBIO) is currently developing a laparoscopic version of their confocal microscopy technology which has similar form factor and optical requirements to what would be needed for beamline use. We propose to leverage DRBIO expertise (Prof. Warren Zipfel) to investigate the feasibility of either adapting our current optics or using an inexpensive aspherical lens system to achieve submicron 3D imaging crystal samples based on natural (tryptophan) or dye-induced flourescence. All four collaborating groups encounter many cases of sample inhomogeneity and crystal imperfection. We propose to also work with a wide range of our users in using microbeams, as part of the MacCHESS service, training, and dissemination missions, to examine crystal quality, to help develop strategies for locating good portions of crystal, and to help users obtain useful data.