title: Influence of human tryptophan hydroxylase 2 N- and C-terminus on enzymatic activity and oligomerization.
abstract: Tryptophan hydroxylase (TPH) catalyses the first and rate limiting step in the biosynthesis of the neurotransmitter serotonin. There are two TPH isoenzymes in humans, encoded by two different genes: TPH1 and the recently described TPH2. We have expressed both human enzymes and various deletion mutants of TPH2 (DeltaN44, DeltaC17, DeltaC19, DeltaC51) in COS7 cells. TPH1 and 2 displayed different kinetic properties with a lower K(m) value of TPH1. Removal of 44 amino acids from the N-terminus of TPH2 resulted in a 3-4-fold increased V(max), which indicates a strong inhibitory function of this part on the enzymes activity. TPH1 and 2 were able to form homooligomers and also heterooligomers with each other. The different deletion mutants (DeltaC17, DeltaC19 and DeltaC51), which lack the putative C-terminal leucine zipper tetramerization domain, existed as monomeric enzymes. While short deletions (DeltaC17 and DeltaC19) hardly changed V(max) values, the DeltaC51 mutant lost 99% of TPH activity. These data identify a region between the C-terminal oligomerization domain and the catalytic domain, which is indispensable for TPH2 activity.
authors.affiliation: Max Delbrück Center for Molecular Medicine, Berlin, GermanyMax Planck Institute for Molecular Genetics, Department for Human Genetics, Berlin, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Tenner
authors.affiliation: Max Delbrück Center for Molecular Medicine, Berlin, GermanyMax Planck Institute for Molecular Genetics, Department for Human Genetics, Berlin, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Walther
authors.affiliation: Max Delbrück Center for Molecular Medicine, Berlin, GermanyMax Planck Institute for Molecular Genetics, Department for Human Genetics, Berlin, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Bader
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D019556:COS Cells; D020134:Catalytic Domain / Q000235:genetics; D002522:Chlorocebus aethiops; D004789:Enzyme Activation / Q000235:genetics; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D009154:Mutation / Q000235:genetics; D011108:Polymers / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D012701:Serotonin / Q000096:biosynthesis*; D014365:Tryptophan Hydroxylase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D011108:Polymers; D012701:Serotonin; C497467:TPH1 protein, human; C494784:TPH2 protein, human; D014365:Tryptophan Hydroxylase