Functional characterization of the S41Y (C2755A) polymorphism of tryptophan hydroxylase 2
Article first published online: 28 JUN 2014
© 2014 International Society for Neurochemistry
Journal of Neurochemistry
Volume 130, Issue 6, pages 748–758, September 2014
How to Cite
J. Neurochem. (2014) 130, 748–758.
- Issue published online: 4 SEP 2014
- Article first published online: 28 JUN 2014
- Accepted manuscript online: 4 JUN 2014 07:37AM EST
- Manuscript Accepted: 23 MAY 2014
- Manuscript Received: 14 MAY 2014
- NIH. Grant Numbers: GM-38931, MH-064756
- genetic polymorphism;
- neurotransmitter biosynthesis;
- PC12 cell;
- protein stability;
Human TPH2 (hTPH2) catalyzes the rate-limiting step in CNS serotonin biosynthesis. We characterized a single-nucleotide polymorphism (C2755A) in the hTPH2 gene that substitutes tyrosine for serine at position 41 in the regulatory domain of the enzyme. This polymorphism is associated with bipolar disorder and peripartum depression in a Chinese population. Recombinant h TPH2 human proteins were expressed in bacteria and also stably expressed in PC12 cells. Following bacterial expression and purification, the tyrosine for serine substitution at position 41 (S41Y) polymorphic enzyme displayed increased Vmax with unchanged Km values. By contrast, enzyme stability was decreased in vitro from 32 min to 4 min (37°C) for the S41Y enzyme (as compared to the wild-type enzyme). The S41Y polymorphism decreased cyclic AMP-dependent protein kinase A-mediated phosphorylation ~ 50% relative to wild-type hTPH2, suggesting that the S41Y mutation may disrupt the post-translational regulation of this enzyme. Transfected PC12 cells expressed hTPH2 mRNA, active protein, and synthesized and released serotonin. Paradoxically, while S41Y-transfected PC12 cells expressed higher levels of hTPH2 than wild type, they synthesized less serotonin. These findings suggest a modified regulation of the S41Y gene variant leading to altered regulation and reduced neurotransmitter synthesis that may contribute to association of the polymorphism with bipolar disorder and depression.
We report the functional implications of a polymorphic human tryptophan hydroxylase-2 gene associated with depression and bipolar disorder. The polymorphic enzyme (serine-41 converted to tyrosine) has increased activity, but decreased enzyme stability and serotonin production. Moreover, cyclic AMP-dependent protein kinase (PKA)-mediated phosphorylation of the mutant enzyme is decreased suggesting modified regulation of the S41Y variant leading to altered serotonin.