title: Cloning and expression of the hypoxanthine-guanine phosphoribosyltransferase gene from Trypanosoma brucei.
abstract: The hypoxanthine-guanine phosphoribosyltransferase (HGPRT) enzyme of Trypanosoma brucei and related parasites provides a rational target for the treatment of African sleeping sickness and several other parasitic diseases. To characterize the T. brucei HGPRT enzyme in detail, the T. brucei hgprt was isolated within a 4.2 kb SalI-KpnI genomic insert and sequenced. Nucleotide sequence analysis revealed an open reading frame of 630 bp that encoded a protein of 210 amino acids with a M(r) = 23.4 kd. After gap alignment, the T. brucei HGPRT exhibited 21-23% amino acid sequence identity, mostly in three clustered regions, with the HGPRTs from human, S. mansoni, and P falciparum, indicating that the trypanosome enzyme was the most divergent of the group. Surprisingly, the T. brucei HGPRT was more homologous to the hypoxanthine phosphoribosyltransferase (HPRT) from the prokaryote V. harveyi than to the eukaryotic HGPRTs. Northern blot analysis revealed two trypanosome transcripts of 1.4 and 1.9 kb, each expressed to equivalent degrees in insect vector and mammalian forms of the parasite. The T. brucei hgprt was inserted into an expression plasmid and transformed into S phi 606 E. coli that are deficient in both HPRT and xanthine-guanine phosphoribosyltransferase activities. Soluble, enzymatically active recombinant T. brucei HGPRT was expressed to high levels and purified to homogeneity by GTP-agarose affinity chromatography. The purified recombinant enzyme recognized hypoxanthine, guanine, and allopurinol, but not xanthine or adenine, as substrates and was inhibited by a variety of nucleotide effectors. The availability of a molecular clone encoding the T. brucei hgprt and large quantities of homogeneous recombinant HGPRT enzyme provides an experimentally manipulable molecular and biochemical system for the rational design of novel therapeutic agents for the treatment of African sleeping sickness and other diseases of parasitic origin.
authors.affiliation: Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland 97201-3098.
authors.forename: T E
authors.initials: TE
authors.lastname: Allen
authors.forename: B
authors.initials: B
authors.lastname: Ullman
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D015870:Gene Expression; D017125:Genes, Protozoan; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D008969:Molecular Sequence Data; D015800:Protozoan Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014346:Trypanosoma brucei brucei / Q000235:genetics*
chemical_list: D017931:DNA Primers; D015800:Protozoan Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D007041:Hypoxanthine Phosphoribosyltransferase