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Functional domains of human tryptophan hydroxylase 2 (hTPH2)

Item Type:Article
Title:Functional domains of human tryptophan hydroxylase 2 (hTPH2)
Creators Name:Carkaci-Salli, N. and Flanagan, J.M. and Martz, M.K. and Salli, U. and Walther, D.J. and Bader, M. and Vrana, K.E.
Abstract:Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in serotonin biosynthesis. A novel gene - termed TPH2 - has recently been described. This gene is preferentially expressed in the central nervous system, while the original TPH1 is the peripheral gene. We have expressed human tryptophan hydroxylase 2 (hTPH2) and two deletion mutants (N150 and N150/C24) using IPTG-free auto-induction in E. coli. This expression system produced active wild type TPH2 with relatively low solubility. The solubility was increased for mutants lacking the N-terminal regulatory domain. The solubility of hTPH2, N150 and N150/C24 are 6.9%, 62% and 97.5%, respectively. Removal of the regulatory domain also produced a more than 6-fold increase in enzyme stability (t1/2 at 37oC). The wild type hTPH2, like other members of the aromatic amino acid hydroxylase superfamily, exists as a homotetramer (236 kDa on size exclusion chromatography). Similarly, N150 also migrates as a tetramer (168 kDa). In contrast, removal of the N-terminal domain and the C terminal, putative leucine zipper tetramerization domain produces monomeric enzyme (39 kDa). Interestingly, removal of the N-terminal regulatory domain did not affect the Michaelis constants for either substrate, but did increase Vmax values. These data identify the N-terminal regulatory domain as the source of hTPH2 instability and reduced solubility.
Keywords:Enzyme Induction, Enzyme Stability, Kinetics, Quaternary Protein Structure, Solubility, Tertiary Protein Structure, Tryptophan Hydroxylase
Source:Journal of Biological Chemistry
Publisher:American Society for Biochemistry and Molecular Biology
Page Range:28105-28112
Date:22 September 2006
Official Publication:https://doi.org/10.1074/jbc.M602817200
PubMed:View item in PubMed

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