text: Cataracts are the primary cause of blindness in humans and mutations in one particular protein, γD-crystallin, have been linked to a number of congenital forms of this disease.  An amino acid mutation, proline (P) to threonine (T) at position 23 of the polypeptide chain has been linked to at least four different forms of this ailment.  SRCD investigations were conducted on the wild-type protein and two variants, the P23T mutant found in the disease, and a related modification, P23S (proline to serine, a chemically similar amino acid to threonine), to establish the nature of the cause of cataract formation.  Two possible reasons were suggested as the causative factor; the reduced solubility of the mutant protein, or an instability in the structure of the protein being introduced by the mutation.  Significantly, because the mutant had limited solubility, lab-based CD machines were only able to provide very noisy spectra and the data were uninterpretable as a result.  However, the SRCD spectra produced had very low noise associated with their data, including the mutant, and showed clearly that the structures of the wild-type, the mutant, and the related protein all had very similar conformations.  These data also established that the mutant retained stability to thermal denaturation, very similar to that of the wild-type protein.  The data confirmed that the causative factor for the cataracts was the reduction in solubility associated with the P23T mutation and not changes in the stability of the protein.
  Because of a high degree of flexibility, it had proven difficult to determine the structure of the extramembranous C-terminal domain of bacterial voltage-gated sodium channels. Using a series of synthesised channels where this C-terminal domain had been truncated, in some cases by a single amino acid difference between the constructs, the Wallace lab used SRCD to successfully identify the structure of this region.