The representation of protein structures

The ball and stick or space-filling approach to the depiction of organic structures is satisfactory when small molecules are concerned, but it becomes too cumbersome for the representation of large molecules. In the case of complex naturally occurring molecules, this level of detail may even obscure the way in which the molecule functions biologically. The problem of structural characterisation in such large molecules will be discussed with respect to proteins, in the following section. 

We have seen that in even very simple materials, the overall pattern of structure in the crystal is not always easy to appreciate just by plotting the contents of a single unit cell. This problem of visualisation is far greater when complex structures such as proteins are considered. One of the more important tasks for the scientists that determined the first protein structures was how to depict the data in such a way that biological activity could be inferred without a loss of chemical or structural information. The way in which 

3Note that this use of the term motif is quite different than that used normally in crystallography - to indicate the unit of structure to be placed at each lattice point to recreate the whole structure. 

Protein studies make up one of the most important and dynamic areas of crystallography, and more information on how these immensely complex structures are described in this fast growing subject area is given in the Bibliography. 

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