Cloning and characterization of a novel enzyme: tyrosine hydroxylase from Schistosoma japonicum

Catecholamines, such as dopamine and noradrenaline, play important roles as neuromuscular transmitters and modulators in all parasitic helminthes, including Schistosoma japonicum. S. japonicum tyrosine hydroxylase (SjTH) was amplified by rapid amplification of cDNA ends polymerase chain reaction that shows strong homology to Schistosoma mansoni tyrosine hydroxylase, the enzyme that catalyzes the first and rate-limiting step in the biosynthesis of catecholamines. The SjTH transcripts encoded the protein of 463 amino acids and a predicted size of 54 kDa. Purified recombinant SjTH as an N-terminal histidine fusion protein expressed in Escherichia coli showed catalytic activity that was confirmed with 3H tyrosine uptake. The purified enzyme was found to have the same absolute requirement for a tetrahydrobiopterin cofactor and similar sensitivity to be inhibited by high concentration of the substrate, tyrosine, as the mammalian enzyme. Also, purified SjTH showed characteristic inhibition by catecholamine products. The phosphorylated peptide from SjTH could interact with Sj14-3-3 signal protein. This evidence indicates that SjTH encodes a functional tyrosine hydroxylase that has catalytic properties similar to those of the mammalian hosts' enzyme, and its catalytic activity could be regulated by a phosphorylated or dephosphorylated form. This demonstration of SjTH further suggests that the parasites have the enzymatic capacity to synthesize catecholamines endogenously.