Mutation of alpha B-crystallin: effects on chaperone-like activity.

A recent paper by Plater et al. [20], showed that the mutation of a single phenylalanine residue F27R in mouse alpha B completely abolished the chaperone-like property of alpha-crystallin when assayed with insulin at 25 degrees C or with gamma-crystallin at 66 degrees C. We have produced the same mutation as well as some additional mutations in human alpha B-crystallin. Our data suggest that the F27R mutation effected the thermal stability of alpha B-crystallin making it unstable at temperatures > or = 60 degrees C. In agreement with the published work, at these temperatures the F27R human recombinant alpha B-crystallin does not protect the target protein from aggregation. When assayed with insulin or alpha-lactalbumin at 25 or 37 degrees C, however, there were no differences in the protective abilities between the native alpha B-crystallin or the F27R mutated human alpha B-crystallin. Several other multiple mutations involving proline residues were also produced. These mutations did not effect the chaperone-like properties of human alpha B-crystallin, but some of them did effect the native molecular weight size as judged by gel filtration chromatography.