Most glycosomal enzymes of Trypanosoma brucei carry a relatively high number of positive charges. In at least 3 of the enzymes some of the charges unique to these enzymes are concentrated in 2 distinct areas on the enzymes' surface, about 4 nm apart [4] and these positively charged structural elements have been suggested to be the site of interaction with the trypanocidal drug Suramin. We have synthesized a series of symmetrical long chain molecules with negative charges or strong dipoles at each end. Several of these compounds inhibited the glycosomal enzymes more strongly than Suramin. They also exhibited a specificity for the trypanosome enzymes, when compared with homologous enzymes from other organisms. By varying the chain length of the active compounds, a 4-nm distance between the molecules' extremes proved optimal for inhibition. Tetra-substituted compounds were better than di-substituted. Modifications introduced at the two ends indicated that a planar orientation, with an amide bond linking a phenyl ring to the chain, is preferred. Inhibition kinetics for some of the enzymes indicated the existence of multi-site interactions with the inhibitors.

The cloned T brucei GAPDH gene was inserted within the B subtilis GAPDH gene, carried by pUC18. Upon transformation of B subtilis by this plasmid, not able to replicate in this host, the whole plasmid was inserted in the resident chromosome, presumably by a single recombination event between homologous, chromosomal and plasmid-borne sequences. The heterologous gene was expressed, as revealed by immunological reaction with monoclonal antibodies, recognizing specifically T brucei GAPDH. T brucei GAPDH, having little or no enzyme activity, comprises about 1.56% of cellular proteins. Peptide mapping showed that a fusion of a 7.5-kDa peptide had occurred to the N-terminal part of T brucei GAPDH. This fused protein is presumably the N-terminal part of B subtilis GAPDH, in agreement with the construction of the integrative plasmid.

Expression of the Trypanosoma brucei ornithine decarboxylase (ODC) gene in Escherichia coli behind the lambda phage PR promoter led to the production of a recombinant enzyme having the same subunit molecular weight as the native enzyme [4]. However, when the same gene is expressed behind the tac promoter or the phoA promoter, the ODCs produced by the transformed E. coli have subunit molecular weights approximately 2 kDa higher than that of the native enzyme. Amino terminal sequencing of the recombinant proteins indicates that the ODC synthesized under control of the lambda PR promoter actually starts at the second methionine (Met23) of the open reading frame, whereas those produced in the latter two cases begin at the first methionine (Met1). Analysis of the 5'-end of T. brucei ODC mRNA supports the conclusion that translation initiates at Met23. We postulate that, for the lambda PR promoter, translation initiates at Met23 instead of Met1 because of the formation of a stable secondary structure in the region of the Met1 and the presence of a good E. coli consensus translation initiation site upstream of Met23. We have constructed a new plasmid using the pho A promoter to express recombinant T. brucei ODC starting at Met23 in large quantities.

Two series of oligopeptides have been synthesized. Their effects on the activity of purified triosephosphate isomerase from Trypanosoma brucei and various other organisms have been studied. Using detailed three-dimensional structure information, the first series consisted of both cyclic and linear hydrophilic peptides that were designed to mimic the beta turns of the subunit interface loops of the trypanosome triosephosphate isomerase dimer. None of these exerted any inhibitory effect. The second series consisted of more hydrophobic cyclic peptides, originally designed to inhibit a hepatic transport system. Several of these were very effective in inhibiting the trypanosome triosephosphate isomerase, but not the homologous enzymes from rabbit, dog, yeast or Escherichia coli. The most active peptide, cyclo[-Trp-Phe-D-Pro-Phe-Phe-Lys(Z)-], exerted 50% inhibitory activity at a concentration of 3 microM. The nature of the inhibitory action of one of these compounds cyclo[-Trp-Tyr(OSO3Na)-D-Pro-Phe-Thr(OSO3Na)-Lys(Z)-] was studied in more detail. Its inhibition was noncompetitive and reversible and more than one peptide was able to bind/active site.

The protozoan haemoflagellate Trypanosoma brucei has two NAD-dependent glyceraldehyde-3-phosphate dehydrogenase isoenzymes, each with a different localization within the cell. One isoenzyme is found in the cytosol, as in other eukaryotes, while the other is found in the glycosome, a microbody-like organelle that fulfils an essential role in glycolysis. The kinetic properties of the purified glycosomal and cytosolic isoenzymes were compared with homologous enzymes from other organisms. Both trypanosome enzymes had pH/activity profiles similar to that of other glyceraldehyde-3-phosphate dehydrogenases, with optimal activity around pH 8.5-9. Only the yeast enzyme showed its maximal activity at a lower pH. The glycosomal enzyme was more sensitive to changes in ionic strength below 0.1 M, while the cytosolic enzyme resembled more the enzymes from rabbit muscle, human erythrocytes and yeast. The affinity for NAD of the glycosomal enzyme was 5-10-fold lower than that of the cytosolic, as well as the other enzymes. A similar, but less pronounced, difference was found for its affinity for NADH. These differences are explained by a number of amino acid substitutions in the NAD-binding domain of the glycosomal isoenzyme. In addition, the effects of suramin, gossypol, agaricic acid and pentalenolactone on the trypanosome enzymes were studied. The trypanocidal drug suramin inhibited both enzymes, but in a different manner. Inhibition of the cytosolic enzyme was competitive with NAD, while in the case of the glycosomal isoenzyme, with NAD as substrate, the drug had an effect both on Km and Vmax. The most potent inhibitor was pentalenolactone, which at micromolar concentrations inhibited the glycosomal enzyme and the enzymes from yeast and Bacillus stearothermophilus in a reversible manner, while the rabbit muscle enzyme was irreversibly inhibited.

Pyruvate kinase from Trypanosoma brucei is a labile enzyme, losing its activity within several hours. In mixtures containing 50 mM triethanolamine buffer, pH 7.2, 25% glycerol and 0.5 mM inorganic phosphate the enzyme remained active and could be purified to homogeneity with a specific activity of 417 units mg−1 and a yield of 65%. The enzyme has an activation energy of 31.9 kJ mol−1. Magnesium and potassium ions are essential for activity. Cobalt or manganese ions replace Mg2+ but this leads to a decrease in maximal velocity. Potassium ions can be substituted by ammonium ions, while sodium ions behave as a competitive inhibitor with respect to both K+ and NH4+. All metal ions studied displayed sigmoidal kinetics. The enzyme is activated, with decreasing efficiency by fructose 2-phosphorothioate 6-phosphate, fructose 2,6-bisphosphate, fructose 1,6-bisphosphate and glucose 1,6-bisphosphate. They all display hyperbolic kinetics. Glycerate 2,3-bisphosphate, glyceraldehyde 3-phosphate, CoASAc, oxalate, AMP, ADP, and ATP inhibit the enzyme. At substrate saturation PK was activated by Pi up to a concentration of 0.8 mM. At higher Pi concentrations the enzyme is inhibited. The enzyme is unaffected by most amino acids, only phenylalanine stimulates and tyrosine inhibits.

The bacterial alkaline phosphatase (phoA) promoter and signal peptide have been used previously to control recombinant expression and secretion of eukaryotic proteins in Escherichia coli. Other reports have shown that this expression system can generate relatively modest levels of active hypoxanthine/guanine phosphoribosyltransferase (HPRT; hypoxanthine phosphoribosyltransferase; IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8), which carries part of the signal peptide but remains in the cytosol of the bacteria. Herein, the phoA promoter without its associated signal peptide is used to regulate expression of the HPRT of Schistosoma mansoni and the ornithine decarboxylase (ODC; L-ornithine carboxy-lyase, EC 4.1.1.17) of Trypanosoma brucei, two enzymes that have been identified as potential targets for antiparasitic chemotherapy. The levels of recombinant expression range from 20% to 60% of the total bacterial protein, and the majority of both recombinant enzymes was soluble. The specific activity for the recombinant trypanosomal ODC was one-third to two-thirds that of the authentic native enzyme and yields were predicted to be 15-30 mg of active enzyme per liter of bacterial culture. The specific activity for the recombinant schistosomal HPRT was equivalent to that for the native enzyme purified from schistosomes and up to 10 mg of enzymatically active HPRT has been purified from a 0.5-liter culture of treated bacteria. These results represent a break-through in recombinant expression of HPRT and ODC.

The protozoan haemoflagellate Trypanosoma brucei, differs from other eukaryotic cells in that it contains nine enzymes involved in glucose and glycerol metabolism which are associated with microbody-like organelles called glycosomes. The information available to date indicates that glycosomal enzymes are synthesized as polypeptides of mature size. For three of them, glyceraldehyde-phosphate dehydrogenase, aldolase and glycerol-3-phosphate dehydrogenase, it has been shown that they are made on free polysomes in the cytosol and are subsequently transferred to the glycosome without any secondary modification. The topogenic signal responsible for import into the glycosome must, therefore, be present in the mature protein. Remarkable differences exist between the latter proteins and other glycolytic enzymes: (i) most glycosomal proteins have an apparent Mr which is 1-5 kDa larger than their homologous counterparts from the cytosol, or from other organisms; (ii) they have a high net positive charge. Based on the modelling of three glycosomal sequences in the respective homologous structures, it is thought that the topogenic signal may consist of a unique insertion, containing one or more basic amino acids which, together with additional positive charges elsewhere, constitute two positive hot spots approximately 4 nm apart on the surface of the protein. Such common elements, unique for the glycolytic enzymes from the Trypanosomatidae, lend themselves as excellent targets for the development of new drugs.