Dear Anna,

I noticed on your page that you will be putting an x-ray diffraction of one of my crystals on my page and I was wondering if you knew the date so I could make sure to look at my page. I know you said it was a monoclinic crystal but whats the difference between monoclinic and the other crystals made? Is there a certain kind of drug we are helping to find?

Katie

Dear Katie,

Here is one of the x-ray image frames of the monoclinic lysozyme from your ground based crystallization trials. It is from Row C Column 6. Your lysozyme stock concentration was at 100 mg/mL. Your buffer was a 0.05M sodium acetate buffer at pH 5.10 and the buffer contained 0.23M NH4NO3. You used 4.25 microliters of buffer containing the ammonium nitrate and 6.75 microliters of the protein. You should now be able to calculate from the total droplet size, and the original concentrations of the protein and the buffer containing the salt, what the concentration of the droplet was at the beginning of the experiment.

There are seven basic crystal systems, and monoclinic is just one of these crystal lattices. The remaining crystal systems are cubic, tetragonal, orthorhombic, hexagonal, rhombohedral, and triclinic. These lattices indicate how the macromolecules pack together and indicate what level of symmetry they contain.

For the most part, when we work with lysozyme, we are using the protein as an investigative tool on which we can build information. We know more about lysozyme, because it crystallizes in so many of the seven basic crystal systems, and because it does so under a variety of conditions. So we use this information, to help us develop theories that we could apply to other more arduous proteins. In many cases this has helped, but because lysozyme is so very unique in its multiplicity of crystal forms and ease of crystallization, everything that we learn about lysozyme may not be able to be applied to other proteins.

Anna

A monoclinic lysozyme crystal is mounted in a glass capillary. The x-ray beam is diffracted through the crystal and the detector behind the crystal records the reflections as shown in the shaded area. The program used to display this image is called d*TREK (D star trek) using a feature called dtdisplay. The resolution arcs (the circles) give you an idea of the highest limit to which the crystal is diffracting in that "particular" frame. We are now "seeing" the effects of the crystal lattice in what is called reciprocal space. So, since this is reciprocal space, the higher resolution would be further out on the target, rather than the bulls-eye center, which shows the low resolution data. The crystal is rotated and another frame is obtained. This frame may be obtained through a different thickness of the crystal, so each frame may have a slightly different highest resolution limit. Once all of the images are collected and a complete data set is collected, the data is then processed using a series of computational iterative methods. This frame resolves to less than 2.0 Angstroms (as shown with spots out to the edge of the dtdisplay "target" screen). That is very good Katie!

A good beginning reference text is Crystallography Made Crystal Clear by Gale Rhodes. ISBN 0-12-587075-2