Carbonic anhydrase as a model for biophysical and physical-organic studies of proteins and protein-ligand binding

Carbonic Anhydrase (CA) is an excellent model for extracting general principles of protein folding. Having the advantage of availability, the ease with which it can be overexpressed in bacteria, the concomitant ability to make site-directed mutations, CA has many aspects of its folding pathway that are prototypical in the folding of proteins. Studies of CA has led to some conclusions such as proteins are not always random coils at high concentrations of denaturants, molten globules can be stable intermediates and investigation of the properties of intermediates that help understand the steps in protein folding and that the pathways of unfolding, folding and yield of correctly folded protein are dependent on the denaturant. In addition, proline isomerization can be the rate-limiting step in protein folding and the conformation of the chain may change both the rate at which the pro bonds isomerize and the accessibility of protein residues to solvent and to proline isomerase. Furthermore, since CA folds in both the presence and absence of chaperones, the effects of chaperone proteins on protein folding can be deduced more easily with CA than with proteins in which folding is not possible in the absence of chaperones.