Mutational Analysis of Catecholamine Binding in Tyrosine Hydroxylase

Changes in Tyrosine Hydroxylase Activity and Dopamine Synthesis in the Nigrostriatal System of Mice in an Acute Model of Parkinson's Disease as a Manifestation of Neurodegeneration and Neuroplasticity

The progressive degradation of the nigrostriatal system leads to the development of Parkinson’s disease (PD). The synthesis of dopamine, the neurotransmitter of the nigrostriatal system, depends on the rate-limiting enzyme, tyrosine hydroxylase (TH). In this study, we evaluated the synthesis of dopamine during periods of neurodegradation and neuroplasticity in the nigrostriatal system on a model of the early clinical stage of PD. It was shown that the concentration of dopamine correlated with activity of TH, while TH activity did not depend on total protein content either in the SN or in the striatum. Both during the period of neurodegeneration and neuroplasticity, TH activity in SN was determined by the content of P19-TH, and in the striatum it was determined by P31-TH and P40-TH (to a lesser extent). The data obtained indicate a difference in the regulation of dopamine synthesis between DA-neuron bodies and their axons, which must be considered for the further development of symptomatic pharmacotherapy aimed at increasing TH activity.

De novo production of the key branch point benzylisoquinoline alkaloid reticuline in yeast

Microbial biosynthesis for plant-based natural products, such as the benzylisoquinoline alkaloids (BIAs), has the potential to address limitations in plant-based supply of established drugs and make new molecules available for drug discovery. While yeast strains have been engineered to produce a variety of downstream BIAs including the opioids, these strains have relied on feeding an early BIA substrate. We describe the de novo synthesis of the major BIA branch point intermediate reticuline via norcoclaurine in Saccharomyces cerevisiae. Modifications were introduced into yeast central metabolism to increase supply of the BIA precursor tyrosine, allowing us to achieve a 60-fold increase in production of the early benzylisoquinoline scaffold from fed dopamine with no supply of exogenous tyrosine. Yeast strains further engineered to express a mammalian tyrosine hydroxylase, four mammalian tetrahydrobiopterin biosynthesis and recycling enzymes, and a bacterial DOPA decarboxylase produced norcoclaurine de novo. We further increased production of early benzylisoquinoline scaffolds by 160-fold through introducing mutant tyrosine hydroxylase enzymes, an optimized plant norcoclaurine synthase variant, and optimizing culture conditions. Finally, we incorporated five additional plant enzymes--three methyltransferases, a cytochrome P450, and its reductase partner--to achieve de novo production of the key branch point molecule reticuline with a titer of 19.2 μg/L. These strains and reconstructed pathways will serve as a platform for the biosynthesis of diverse natural and novel BIAs.

Common somatic alterations identified in maffucci syndrome by molecular karyotyping

Maffucci syndrome (MS) is a rare congenital disorder characterized by multiple central cartilaginous tumors (enchondromas) in association with cutaneous spindle cell hemangiomas. These patients have a high incidence of malignant transformation. No familial case is known and the etiopathogenic cause remains unknown. In enchondromatosis (Ollier disease, OD), which is comprised of enchondromas only, 4 mutations in the PTHR1 gene have been identified in 4 patients; 3 were somatic and 1 was germline. No PTHR1 mutations have been detected in MS, whereas somatic IDH1 and, more rarely, IDH2 mutations have been observed in 77% of patients with MS and 81% of patients with OD. These genetic alterations are shared with other tumors, including glioma, leukemia and carcinoma. To search for underlying somatic genomic causes, we screened MS tissues using Affymetrix SNP-chips. We looked for CNVs, LOH and uniparental isodisomy (UPID) by performing pairwise analyses between allelic intensities in tumoral DNA versus the corresponding blood-extracted DNA. While common chromosomal anomalies were absent in constitutional DNA, several shared CNVs were identified in MS-associated tumors. The most frequently encountered somatic alterations were localized in 2p22.3, 2q24.3 and 14q11.2, implicating these chromosomal rearrangements in the formation of enchondromas and spindle cell hemangiomas in MS. In one chondrosarcoma specimen, large amplifications and/or deletions were observed in chromosomes 3, 6, 9, 10, 12, 13, and 19. Some of these genetic changes have been reported in other chondrosarcomas suggesting an etiopathogenic role. No LOH/UPID was observed in any Maffucci tissue. Our findings identify frequent somatic chromosomal rearrangements on 2p22.3, 2q24.3 and 14q11.2, which may unmask mutations leading to the lesions pathognomonic of MS.

Complex molecular regulation of tyrosine hydroxylase

Tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, is strictly controlled by several interrelated regulatory mechanisms. Enzyme synthesis is controlled by epigenetic factors, transcription factors, and mRNA levels. Enzyme activity is regulated by end-product feedback inhibition. Phosphorylation of the enzyme is catalyzed by several protein kinases and dephosphorylation is mediated by two protein phosphatases that establish a sensitive process for regulating enzyme activity on a minute-to-minute basis. Interactions between tyrosine hydroxylase and other proteins introduce additional layers to the already tightly controlled production of catecholamines. Tyrosine hydroxylase degradation by the ubiquitin-proteasome coupled pathway represents yet another mechanism of regulation. Here, we revisit the myriad mechanisms that regulate tyrosine hydroxylase expression and activity and highlight their physiological importance in the control of catecholamine biosynthesis.

Tyrosine hydroxylase: regulation by feedback inhibition and phosphorylation

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of the catecholamines dopamine, noradrenaline, and adrenaline. In response to short-term stimuli, TH activity is regulated by feedback inhibition by the catecholamines and relief of that inhibition by phosphorylation. This chapter examines the current understanding of these regulatory mechanisms and the roles that they play in different catecholaminergic cells. This chapter also examines hierarchical phosphorylation in TH and how it provides a mechanism for the differential regulation of the major human TH isoforms.