Solving a Macromolecular Crystal Structure:
A Real-Life Example
Solving a macromolecular crystal structure involves several sets of computations. Each crystal structural problem is unique, so it is an over-simplification to claim that one procedure, rigidly followed, will lead to a solution. Nevertheless, the process involved is much more clearly deliniated beforehand than with many scientific enterprises. Discoveries usually come about when analyzing a structure rather than in developing novel procedures for its solution. Similarly, a very interesting structure might prove comparatively easy to solve, whereas a crystal structural solution might be very difficult yet lead to an utterly boring result.
In general, structural solution of a crystallized macromolecule will proceed along the following lines. We'll provide real-time examples at each step, starting with step 1. We'll use CCP4 programs since they are freely available to academics as unrestricted downloads, and also CNS. With CNS, I'll have you do this with just one derivative to show you that this can work too. For tips on installing this software on a PC (running Linux) or a Mac (running OS X), go here. These programs also have their own tutorials that are definitely worth working through.
Steps in solving the hammerhead ribozyme crystal structure using CCP4:
Steps in solving the hammerhead ribozyme crystal structure using CNS:
1. Scaling Native to Derivative Data
2. Finding Heavy Atom Sites3. Calculating Phases
4. Solvent-Flattening, Map Calculation and Display
5. Displaying the Electron Density Map and Model Building [under construction]
6. Crystallographic Refinement [under construction]
2. Finding heavy atom sites
3. Calculating Phases
4. Solvent-Flattening, Map Calculation and Display
5. Model building and refinement
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