Molecular and biochemical characterisation of arginine kinases in Haemonchus contortus and Teladorsagia circumcincta.

Full length cDNA encoding arginine kinases (AK) were cloned from Teladorsagia circumcincta (TcAK) and Haemonchus contortus (HcAK). The TcAK and HcAK cDNA (1080 bp) encoded 360 amino acid proteins. The predicted amino acid sequence showed 99% similarity with each other and 94% with a Caenorhabditis elegans AK. Soluble N-terminal His-tagged AK proteins were expressed in Escherichia coli strain BL21, purified and characterised. All binding sites were completely conserved in both proteins. The recombinant TcAK and HcAK had very similar kinetic properties: K(m) arginine was 0.35 mM, K(m) ATP was 0.8-0.9 mM and the pH optima were pH 7.5. Arginine analogues strongly inhibited recombinant enzyme activities (up to 80%), whilst other amino acids decreased activities by a maximum of 20%. TcAK and HcAK are potential vaccine candidates because of the strong antigenicity of invertebrate phosphagens and kinases and presence in metabolically active parts of the worm.

Sarcosine metabolism in Haemonchus contortus and Teladorsagia circumcincta.

Sarcosine (N-methylglycine) is an intermediate in glycine degradation and can also be synthesised from glycine in mammals. Sarcosine metabolism in Haemonchus contortus and Teladorsagia circumcincta differed from that of mammals in that creatinase activity was present and sarcosine was demethylated only by sarcosine oxidase (SOX) and not by sarcosine dehydrogenase (SDH). The mean SOX activity was 30 nmolmin(-1)mg(-1) protein in homogenates of L3 and adult worms of both parasites and the apparent Km for sarcosine was 1.1 mM. Addition of 2 mM Cd(2+) inhibited activity by 30%. There was no SDH activity with either NAD(+) or NADP(+) as co-factor. Mean creatinase activity in L3 T. circumcincta and adult worms of both species was 31±6 nmolmin(-1)mg(-1) protein, but was undetectable in L3 H. contortus. Activity was inhibited by up to 70% by Cu(2+), Fe(2+), Fe(3+) and Zn(2+). Possessing creatinase would allow host creatine to be incorporated into amino acids by the parasites.

Lysine catabolism in Haemonchus contortus and Teladorsagia circumcincta.

Catabolism of lysine through the pipecolate, saccharopine and cadaverine pathways has been investigated in L3 and adult Haemonchus contortus and Teladorsagia circumcincta. Both enzymes of the saccharopine pathway (lysine ketoglutarate reductase (LKR) and saccharopine dehydrogenase (SDH)) were active in L3 and adult worms of both species. All three enzymes which catabolise lysine to α-amino adipic semialdehyde via pipecolate (lysine oxidase (LO), Δ(1)-piperideine-2-carboxylate reductase (Pip2CR) and pipecolate oxidase (PipO)) were present in adult worms, whereas the pathway was incomplete in L3 of both species; Pip2CR activity was not detected in the L3 of either parasite species. In adult worms, the saccharopine pathway would probably be favoured over the pipecolate pathway as the K(m) for lysine was lower for LKR than for LO. Neither lysine dehydrogenase nor lysine decarboxylase activity was detected in the two parasite species. Enzyme activities and substrate affinities were higher for all five enzymes in adult worms than in L3. An unexpected finding was that both LKR and SDH were dual co-factor enzymes and not specific for either NAD(+) or NADP(+), as is the case in other organisms. This novel property of LKR/SDH suggests it could be a good candidate for anthelmintic targeting.

Molecular and biochemical characterisation of a Teladorsagia circumcincta glutamate dehydrogenase.

A full length cDNA encoding glutamate dehydrogenase was cloned from Teladorsagia circumcincta (TcGDH). The TcGDH cDNA (1614 bp) encoded a 538 amino acid protein. The predicted amino acid sequence showed 96% and 93% similarity with Haemonchus contortus and Caenorhabditis elegans GDH, respectively. A soluble N-terminal 6xHis-tagged GDH protein was expressed in the recombinant Escherichia coli strain BL21 (DE3) pGroESL, purified and characterised. The recombinant TcGDH had similar kinetic properties to those of the enzyme in homogenates of T. circumcincta, including greater activity in the aminating than deaminating reaction. Addition of 1mM ADP and ATP increased activity about 3-fold in the deaminating reaction, but had no effect in the reverse direction. TcGDH was a dual co-factor enzyme that operated both with NAD(+) and NADP(+), GDH activity was greater in the deaminating reaction with NADP(+) as co-factor and more with NADH in the aminating reaction.

Enzymes of the ornithine-glutamate-proline pathway in the sheep abomasal nematode parasites Haemonchus contortus and Teladorsagia circumcincta.

A fully functional ornithine-glutamate-proline pathway was detected in L3 and adult Haemonchus contortus and Teladorsagia circumcincta, making the parasites capable of interconversion of these amino acids. Ornithine aminotransferase (OAT) (E.C. 2.6.1.13) was a reversible pyridoxal-5-phosphate (PLP)-dependent enzyme with an optimum pH 8.5. Hydroxylamine completely inhibited OAT activity in both parasites. For all five enzymes, substrate affinity was similar for each species and life cycle stage, the notable exceptions being the nearly 10-fold lower affinity for Δ(1)-pyrroline-5-carboxylate (P5C) of P5C reductase (E.C. 1.5.1.2) in adult T. circumcincta and about half for P5C for L3 H. contortus P5C dehydrogenase (E.C. 1.5.1.12). P5C synthase (E.C. 1.2.1.41) activity was similar with either NADPH or NADH as co-factor. Proline oxidase (E.C. 1.5.99.8) was a co-factor independent enzyme with an optimal pH 8.5. Despite similarities to those in the host, enzymes of this pathway may still be useful as control targets if they differ antigenically, as a supply of proline is necessary for cuticle formation.

Glutamate synthase, but not GABA shunt enzymes, contributes to nitrogen metabolism of the sheep abomasal nematode parasites Haemonchus contortus and Teladorsagia circumcincta.

Glutamate synthase (E.C. 1.4.1.14) (GOGAT) activity was not detectable in L3 Haemonchus contortus, but was present in L3 Teladorsagia circumcincta and adult worms of both species. GOGAT activity was inhibited by 80% by azaserine. Activity (nmol min(-1) mg(-1) protein) was 33-59 in adult H. contortus, 51-91 in adult T. circumcincta and 24-41 in L3 T. circumcincta, probably depending on exposure to ammonia, as incubation with 1mM NH(4)Cl doubled GOGAT activity. The pH optimum was 7.5 in both species. Either NAD or NADP acted as co-factor. The mean apparent K(m) for 2-oxoglutarate was 0.7 (0.5-0.9) mM and for glutamine was 1.0 (0.5-1.7) mM for different homogenates. There was no detectable activity in whole parasite homogenates of glutamate decarboxylase (E.C. 4.1.1.15) or succinic semialdehyde dehydrogenase (E.C. 1.2.1.24), the first and third enzymes of the GABA shunt, respectively, suggesting that the GABA shunt is not important in general metabolism in these species.

Arginine metabolism in the sheep abomasal nematode parasites Haemonchus contortus and Teladorsagia circumcincta.

The ornithine urea cycle, polyamine synthesis, nitric oxide synthesis and metabolism of arginine to putrescine have been investigated in L3 and adult Haemonchus contortus and Teladorsagia circumcincta. Neither parasite had a detectable arginine deiminase/dihydrolase pathway nor a functional ornithine urea cycle. Nitric oxide synthase was present in central and peripheral nerves, but was not detected in whole parasite homogenates. Both arginase (E.C. 3.5.3.1) and agmatinase (E.C. 3.5.3.11) activities were present in both species. Arginase did not require added Mn(2+) and had an optimal pH of 8.5. Polyamine metabolism differed in the two species and from that in mammals. Ornithine decarboxylase (E.C. 4.1.1.17) was present in both parasites, but no arginine decarboxylase (E.C. 4.1.1.19) activity was detected in T. circumcincta. The flexibility of synthesis of putrescine in H. contortus may make this pathway less useful as a target for parasite control than in T. circumcincta, in which only the ornithine decarboxylase pathway was detected.