High level expression of rat gamma-D-crystallin in Escherichia coli

Gamma-crystallins have been implicated in various kinds of cataracts. In order to facilitate studies elucidating the molecular mechanism of cataractogenesis, large quantities of rat recombinant gamma-D-crystallin were produced in E coli. A full length cDNA clone coding for gamma-D-crystallin was isolated from a rat lens lambda gt11 cDNA library using a synthetic oligonucleotide as a probe. The coding region of this cDNA was inserted into a cloning vector pKK233-2 under the control of the trc promoter. The resulting construct, pKKCR91, was transfected into E coli to produce rat gamma-D-crystallin in an amount of 10-15% of the total bacterial proteins. The crystallin produced was purified to an apparent homogeneity as judged by SDS gel electrophoresis. The sequence of the N-terminal 11 amino acids of the purified crystallin was determined, showing that it is completely identical to that predicted from the cDNA sequence. Measurements of the far-UV CD spectra also revealed that recombinant rat gamma-D-crystallin thus produced retains a native conformational structure.