Stabilization of the blue copper center by placing it within a very rigid structure, such as that in plastocyanin, was also needed. Application of these principles allowed him to alter the single Fe center of thioredoxin from an organic redox center to a metal ion one in a straightforward fashion. As Homme's work illustrated, many effects of point mutations cannot be rationally predicted a priori. An alternate way of looking at the effect of mutations on the composition of structural ensembles rather than on a discrete static structure may help to understand some of these effects. His program has been able to pinpoint mutations that affect activity by changing the predicted ensemble while having little effect on the crystal structure.
Mutants can also change the structure of the denatured state.
The structure of RNAs selected for specific binding properties has proved to be as complex as that of proteins. She presented three different structures of small RNAs which each required years to solve, isotopic labeling or new pulse sequences. In contrast, for a UGAA tetraloop at the end of a stem structure from 16S like ribosomal RNA, the G base stacked over the U and the two A bases overlapped to form a very stable structure. For her third example, a Tetrahymena RNA-receptor for a GAAA tetraloop, the structure of the bound RNA was known from a crystal structure of the complex. They found that the free RNA receptor molecule contained an adenine platform at the docking site for the tetraloop.