Interaction of phosphorylated tryptophan hydroxylase with 14-3-3 proteins.
Rabbit brain tryptophan hydroxylase (TPH) has been expressed in insect cells (Spodoptera frugiperda) as a histidine-tagged enzyme. The specific activity of the purified fusion enzyme is 80 nmol of 5-hydroxytryptophan/min/mg. Multifunctional regulatory 14-3-3 proteins were purified from fresh bovine brain. Phosphorylation and 14-3-3 proteins play important roles in the regulation of TPH activity. We have found that phosphorylation of TPH by cAMP-dependent protein kinase increased the activity of the hydroxylase by 25-30% and that 14-3-3 proteins increased the hydroxylase activity of phosphorylated TPH by approximately 45%. Under these conditions, the 14-3-3 proteins were not phosphorylated, and unphosphorylated TPH was not activated by 14-3-3 proteins. Surface plasmon resonance analysis demonstrated that 14-3-3 proteins bind to phosphorylated TPH with an affinity constant (Ka) of 4.5 x 10(7) M-1. Binding studies using affinity chromatography also showed that 14-3-3 proteins interact with phosphorylated TPH. The dephosphorylation of TPH by protein phosphatase-1 was inhibited by 14-3-3 proteins. Our results demonstrate that 14-3-3 proteins form a complex with phosphorylated brain TPH, thereby increasing its enzymatic activity and inhibiting its dephosphorylation.[1]References
- Interaction of phosphorylated tryptophan hydroxylase with 14-3-3 proteins. Banik, U., Wang, G.A., Wagner, P.D., Kaufman, S. J. Biol. Chem. (1997) [Pubmed]
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