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Functional characterization of the S41Y (C2755A) polymorphism of tryptophan hydroxylase 2
Author(s) -
CarkaciSalli Nurgul,
Salli Ugur,
Tekin Izel,
Hengst Jeremy A.,
Zhao Moe K.,
Gilman T. Lee,
Andrews Anne M.,
Vrana Kent E.
Publication year - 2014
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/jnc.12779
Subject(s) - tph2 , tryptophan hydroxylase , tyrosine hydroxylase , serine , biology , tyrosine , enzyme , microbiology and biotechnology , tryptophan , serotonin , biochemistry , amino acid , receptor , serotonergic
Human TPH2 ( hTPH 2) catalyzes the rate‐limiting step in CNS serotonin biosynthesis. We characterized a single‐nucleotide polymorphism (C2755A) in the hTPH 2 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 V max with unchanged K m 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 hTPH 2, suggesting that the S41Y mutation may disrupt the post‐translational regulation of this enzyme. Transfected PC12 cells expressed hTPH 2 mRNA , active protein, and synthesized and released serotonin. Paradoxically, while S41Y‐transfected PC12 cells expressed higher levels of hTPH 2 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.