A Strategy for the Creation of Mutations in Human HPRT-cDNA and the Expression of Recombinant Proteins in E.Coli

Abstract

The Lesch-Nyhan syndrome and gouty arthritis (due to the overproduction of urate), are manifestations of deficiencies of the purine salvage enzyme, HPRT. The molecular lesions responsible for the deficiency of this enzyme activity have been well characterised for numerous human patients. The observed mutations occur over the entire coding region of the HPRT gene, giving rise to proteins with altered amino acid sequence. However, knowledge of the location of these mutations has contributed little information about the active site of the enzyme. We are currently using chemical modification, together with site-directed mutagenesis, to study the relationship between structure and function of the human HPRT enzyme. To this end we have expressed the recombinant protein from normal human HPRT-cDNA sequence in E.coli (Free et al., 1990). The recombinant protein was found to have similar properties to human HPRT isolated from erythrocyte and lymphoblast cells. A strategy, using PCR amplification (Saiki et al.,1988) and splicing by overlap extension (Horton et al.,1989), has been used to reproduce the natural mutations which occur in two patients with partial deficiency of HPRT activity. Expression of these mutant proteins was undertaken to (a) compare the properties of the recombinant and naturally occurring enzymes and (b) produce larger amounts of recombinant enzyme for more detailed studies.