Direct binding of GTP cyclohydrolase and tyrosine hydroxylase: Regulatory interactions between key enzymes in dopamine biosynthesis

Kevin M. Bowling, Zhinong Huang, Dong Xu, Faiza Ferdousy, Christopher D. Funderburk, Nirmala Karnik, Wendi Neckameyer, Janis M. O'Donnell

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


The signaling functions of dopamine require a finely tuned regulatory network for rapid induction and suppression of output. A key target of regulation is the enzyme tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis, which is activated by phosphorylation and modulated by the availability of its cofactor, tetrahydrobiopterin. The first enzyme in the cofactor synthesis pathway, GTP cyclohydrolase I, is activated by phosphorylation and inhibited by tetrahydrobiopterin. We previously reported that deficits in GTP cyclohydrolase activity in Drosophila heterozygous for mutant alleles of the gene encoding this enzyme led to tightly corresponding diminution of in vivo tyrosine hydroxylase activity that could not be rescued by exogenous cofactor. We also found that the two enzymes could be coimmunoprecipitated from tissue extracts and proposed functional interactions between the enzymes that extended beyond provision of cofactor by one pathway for another. Here, we confirm the physical association of these enzymes, identifying interacting regions in both, and we demonstrate that their association can be regulated by phosphorylation. The functional consequences of the interaction include an increase in GTP cyclohydrolase activity, with concomitant protection from end-product feedback inhibition. In vivo, this effect would in turn provide sufficient cofactor when demand for catecholamine synthesis is greatest. The activity of tyrosine hydroxylase is also increased by this interaction, in excess of the stimulation resulting from phosphorylation alone. Vmax is elevated, with no change in Km. These results demonstrate that these enzymes engage in mutual positive regulation.

Original languageEnglish
Pages (from-to)31449-31459
Number of pages11
JournalJournal of Biological Chemistry
Issue number46
StatePublished - Nov 14 2008


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