XtalScreens help

XtalScreens is a utility for looking up recipes for commercial crystallisation screen kits.
It can be run interactively from http://xray.bmc.uu.se/markh/php/xtalscreens.php, or called from another program.
It was written as a service for the Xtrack crystallographic database system.

Data :

The data has been mined from the manufacturers' web sites, and they are responsible for the conventions, spellings and abbreviations used, which differ between (and sometimes within) companies. When used within Xtrack however, the program tries to reduce those inconsistencies (and fit a complete plate on one page) by substituting standard abbreviations.

The colours used indicate the column in which the component was found in the companies' formatted data sheets, so all blue text was found in column 1, green in column 2, orangey in column 3. Sometimes this is interesting, in that similarly-coloured components will have similar functions, so blue may indicate a salt, green a buffer, and orangey a precipitant, but unfortunately there is little consistency. Whether or not a final pH value appears is also inconsistent.

Interactive lookup :

The user specifies the screen name and the program fetches the appropriate recipe from the database kept on the server at Uppsala University.
The format and font size can also be chosen to make printing more flexible. Formats include 'Table' which presents the data in a table that assumes that the screen is used in a plate that is wider than it is high (eg 6 wells across and 4 wells down); 'Lines' which simply lists the solutions one per line on the page; and 'Lines (CxR)' where C and R represent the number of rows and columns on the plate, in which case a well position (A1, B3 etc) will be printed out along with the recipe on each line. This allows well assignments to be quickly found which ever way the plate is filled (across rows first, or down columns). pHsort will list the wells sorted by buffer pH, for visual searching for specific conditions.
Selecting "Expand List" from the bottom of the menu list, or clicking on the "Show All Screens" link, gives a page with data on all the available screens, including the full name and the abbreviation used by XtalScreens.

Searching and Sorting :

If you click on the "Search All Screens" link, you will taken to the search and sort interface, where you can choose which solutions you would like to see by entering a series of keywords that must be present in the recipe descriptions. The test is done both before and after substituting standard abbreviations, to allow for inconsistences in company naming conventions.
You can choose which screens to look in by entering a space-separated list of the abbreviated screen names in the "Screens" box. The abbreviated names are those used in the "Show all screens" page.
You can also choose how the resulting list will be sorted, using any of the fields that may be present. Note however that the field names can be misleading, as some companies may consider a component as a salt, another as a buffer. The different field names really only represent different columns in the recipe, so this sort feature is not really very useful.
If you use the input box labelled "exact search" instead of the "keywords" box, only exact matches will be returned. That means that the string that you enter must appear must be delimited by white space or a line start or end in the recipe. This allows you for instance to find only PEG 400, and not PEG 4000. This test is case insensitive and if specified, entries in the keyword box are ignored.

Programmed lookup :

Normally the result comes in a nicely-formatted little box, but a simpler format, which is suitable for interrogation by a remote program, can be returned by calling as follows. Note that the abbreviated name must be passed in the call.


For example :

or :


A note on the mini24 screen :

When the Jancarik&Kim screen was first published, our lab made up solutions and numbered them according to their order in the original paper. Then we started buying the Hampton kit, which uses the same ordering. and now we also use the mini24 screen from Molecular Dimensions. But they have chosen a different order for the solutions, so as of 28 march 2007, the xtalscreens database entry for the mini24 reflects this new ordering.

by Mark Harris