Intracellular stability of tyrosine hydroxylase: phosphorylation and proteasomal digestion of the enzyme

Enhancement of β-Caryophyllene Biosynthesis in Saccharomyces cerevisiae via Synergistic Evolution of β-Caryophyllene Synthase and Engineering the Chassis

β-Caryophyllene is a plant-derived bicyclic sesquiterpene with multiple biological functions. β-Caryophyllene production by engineered Saccharomyces cerevisiae represents a promising technological route. However, the low catalytic activity of β-caryophyllene synthase (CPS) is one of the main restrictive factors for β-caryophyllene production. Here, directed evolution of the Artemisia annua CPS was performed, and variants of CPS enhancing the β-caryophyllene biosynthesis in S. cerevisiae were obtained, in which an E353D mutant enzyme presented large improvements in Vmax and Kcat. The Kcat/Km of the E353D mutant was 35.5% higher than that of wild-type CPS. Moreover, the E353D variant exhibited higher catalytic activity in much wider pH and temperature ranges. Thus, both the higher catalytic activity and the robustness of the E353D variant contribute to the 73.3% increase in β-caryophyllene production. Furthermore, the S. cerevisiae chassis was engineered by overexpressing genes related to β-alanine metabolism and MVA pathway to enhance the synthesis of the precursor, and ATP-binding cassette transporter gene variant STE6T1025N to improve the transmembrane transport of β-caryophyllene. The combined engineering of CPS and chassis resulted in 70.45 mg/L of β-caryophyllene after 48 h of cultivation in a test tube, which was 2.93-fold of that of the original strain. Finally, a β-caryophyllene yield of 594.05 mg/L was obtained by fed-batch fermentation, indicating the potential of β-caryophyllene production by yeast.

Behavior of Neural Cells Post Manufacturing and After Prolonged Encapsulation within Conductive Graphene-Laden Alginate Microfibers

Engineering conductive 3D cell scaffoldings offer advantages toward the creation of physiologically relevant platforms with integrated real-time sensing capabilities. Dopaminergic neural cells are encapsulated into graphene-laden alginate microfibers using a microfluidic approach, which is unmatched for creating highly-tunable microfibers. Incorporating graphene increases the conductivity of the alginate microfibers by 148%, creating a similar conductivity to native brain tissue. The cell encapsulation procedure has an efficiency of 50%, and of those cells, ≈30% remain for the entire 6-day observation period. To understand how the microfluidic encapsulation affects cell genetics, tyrosine hydroxylase, tubulin beta 3 class 3, interleukin 1 beta, and tumor necrosis factor alfa are analyzed primarily with real-time reverse transcription-quantitative polymerase chain reaction and secondarily with enzyme-linked immunosorbent assay, immediately after manufacturing, after encapsulation in polymer matrix for 6 days, and after encapsulation in the graphene-polymer composite for 6 days. Preliminary data shows that the manufacturing process and combination with alginate matrix affect the expression of the studied genes immediately after manufacturing. In addition, the introduction of graphene further changes gene expressions. Long-term encapsulation of neural cells in alginate and 6-day exposure to graphene also leads to changes in gene expressions.

Trojan Horse Delivery of 4,4'-Dimethoxychalcone for Parkinsonian Neuroprotection

Parkinson's disease (PD) is characterized by the progressive deterioration of dopamine (DA) neurons, and therapeutic endeavors are aimed at preventing DA loss. However, lack of effective brain delivery approaches limits this strategy. In this study, a "Trojan horse" system is used for substantia nigra-targeted delivery of a blood brain barrier-penetrating peptide (RVG29) conjugated to the surface of nanoparticles loaded with the natural autophagy inducer 4,4'-dimethoxychalcone (DMC) (designated as RVG-nDMC). Here, the neuroprotective effects of DMC are demonstrated in PD. Specifically, RVG-nDMC penetrates the blood brain barrier with enhanced brain-targeted delivery efficiency and is internalized by DA neurons and microglia. In vivo studies demonstrate that RVG-nDMC ameliorates motor deficits and nigral DA neuron death in PD mice without causing overt adverse effects in the brain or other major organs. Moreover, RVG-nDMC reverses tyrosine hydroxylase ubiquitination and degradation, alleviates oxidative stress in DA neurons, and exerts antiinflammatory effects in microglia. The "Trojan horse" strategy for targeted delivery of DMC thus provides a potentially powerful and clinically feasible approach for PD intervention.

The quaternary structure of human tyrosine hydroxylase: effects of dystonia-associated missense variants on oligomeric state and enzyme activity

Abstract

Tyrosine hydroxylase (TH) is a multi‐domain, homo‐oligomeric enzyme that catalyses the rate‐limiting step of catecholamine neurotransmitter biosynthesis. Missense variants of human TH are associated with a recessive neurometabolic disease with low levels of brain dopamine and noradrenaline, resulting in a variable clinical picture, from progressive brain encephalopathy to adolescent onset DOPA‐responsive dystonia (DRD). We expressed isoform 1 of human TH (hTH1) and its dystonia‐associated missense variants in E. coli, analysed their quaternary structure and thermal stability using size‐exclusion chromatography, circular dichroism, multi‐angle light scattering, transmission electron microscopy, small‐angle X‐ray scattering and assayed hydroxylase activity. Wild‐type (WT) hTH1 was a mixture of enzymatically stable tetramers (85.6%) and octamers (14.4%), with little interconversion between these species. We also observed small amounts of higher order assemblies of long chains of enzyme by transmission electron microscopy. To investigate the role of molecular assemblies in the pathogenesis of DRD, we compared the structure of WT hTH1 with the DRD‐associated variants R410P and D467G that are found in vicinity of the predicted subunit interfaces. In contrast to WT hTH1, R410P and D467G were mixtures of tetrameric and dimeric species. Inspection of the available structures revealed that Arg‐410 and Asp‐467 are important for maintaining the stability and oligomeric structure of TH. Disruption of the normal quaternary enzyme structure by missense variants is a new molecular mechanism that may explain the loss of TH enzymatic activity in DRD. Unstable missense variants could be targets for pharmacological intervention in DRD, aimed to re‐establish the normal oligomeric state of TH.

Human tyrosine hydroxylase in Parkinson's disease and in related disorders

Parkinson's disease (PD) is an aging-related movement disorder mainly caused by a deficiency of neurotransmitter dopamine (DA) in the striatum of the brain and is considered to be due to progressive degeneration of nigro-striatal DA neurons. Most PD is sporadic without family history (sPD), and there are only a few percent of cases of young-onset familial PD (fPD, PARKs) with the chromosomal locations and the genes identified. Tyrosine hydroxylase (TH), tetrahydrobiopterin (BH4)-dependent and iron-containing monooxygenase, catalyzes the conversion of L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA), which is the initial and rate-limiting step in the biosynthesis of catecholamines (DA, noradrenaline, and adrenaline). PD affects specifically TH-containing catecholamine neurons. The most marked neurodegeneration in patients with DA deficiency is observed in the nigro-striatal DA neurons, which contain abundant TH. Accordingly, TH has been speculated to play some important roles in the pathophysiology in PD. However, this decrease in TH is thought to be secondary due to neurodegeneration of DA neurons caused by some as yet unidentified genetic and environmental factors, and thus, TH deficiency may not play a direct role in PD. This manuscript provides an overview of the role of human TH in the pathophysiology of PD, covering the following aspects: (1) structures of the gene and protein of human TH in relation to PD; (2) similarity and dissimilarity between the phenotypes of aging-related sPD and those of young-onset fPD or DOPA-responsive dystonia due to DA deficiency in the striatum with decreased TH activity caused by mutations in either the TH gene or GTP cyclohydrolase I (GCH1) gene; and (3) genetic variants of the TH gene (polymorphisms, rare variants, and mutations) in PD, as discovered recently by advanced genome analysis.

Aldehyde dehydrogenase 2 activation and coevolution of its εPKC-mediated phosphorylation sites

Background

Mitochondrial aldehyde dehydrogenase 2 (ALDH2) is a key enzyme for the metabolism of many toxic aldehydes such as acetaldehyde, derived from alcohol drinking, and 4HNE, an oxidative stress-derived lipid peroxidation aldehyde. Post-translational enhancement of ALDH2 activity can be achieved by serine/threonine phosphorylation by epsilon protein kinase C (εPKC). Elevated ALDH2 is beneficial in reducing injury following myocardial infarction, stroke and other oxidative stress and aldehyde toxicity-related diseases. We have previously identified three εPKC phosphorylation sites, threonine 185 (T185), serine 279 (S279) and threonine 412 (T412), on ALDH2. Here we further characterized the role and contribution of each phosphorylation site to the enhancement of enzymatic activity by εPKC.

Methods

Each individual phosphorylation site was mutated to a negatively charged amino acid, glutamate, to mimic a phosphorylation, or to a non-phosphorylatable amino acid, alanine. ALDH2 enzyme activities and protection against 4HNE inactivation were measured in the presence or absence of εPKC phosphorylation in vitro. Coevolution of ALDH2 and its εPKC phosphorylation sites was delineated by multiple sequence alignments among a diverse range of species and within the ALDH multigene family.

Results

We identified S279 as a critical εPKC phosphorylation site in the activation of ALDH2. The critical catalytic site, cysteine 302 (C302) of ALDH2 is susceptible to adduct formation by reactive aldehyde, 4HNE, which readily renders the enzyme inactive. We show that phosphomimetic mutations of T185E, S279E and T412E confer protection of ALDH2 against 4HNE-induced inactivation, indicating that phosphorylation on these three sites by εPKC likely also protects the enzyme against reactive aldehydes. Finally, we demonstrate that the three ALDH2 phosphorylation sites co-evolved with εPKC over a wide range of species. Alignment of 18 human ALDH isozymes, indicates that T185 and S279 are unique ALDH2, εPKC specific phosphorylation sites, while T412 is found in other ALDH isozymes. We further identified three highly conserved serine/threonine residues (T384, T433 and S471) in all 18 ALDH isozymes that may play an important phosphorylation-mediated regulatory role in this important family of detoxifying enzymes.

Conclusion

εPKC phosphorylation and its coevolution with ALDH2 play an important role in the regulation and protection of ALDH2 enzyme activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-016-0312-x) contains supplementary material, which is available to authorized users.

Inhibition of deubiquitinating activity of USP14 decreases tyrosine hydroxylase phosphorylated at Ser19 in PC12D cells

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in catecholamine biosynthesis, and its stability is a fundamental factor to maintain the level of the catecholamines in cells. However, the intracellular stability determined by the degradation pathway remains unknown. In this study, we investigated the mechanism by which phosphorylation of TH affected the proteasome pathway. The inhibition of proteasomes by MG-132 increased the percentage of TH molecules phosphorylated at their Ser19, Ser31 and/or Ser40 among the total TH proteins to about 70% in PC12D cells over a 24-hr period; although the percentage of phosphorylated TH molecules was about 20% under basal conditions. Moreover, the inhibition of proteasomes by epoxomicin with high specificity increased primarily the quantity of TH molecules phosphorylated at their Ser19. The phosphorylation of Ser19 potentiated Ser40 phosphorylation in cells by a process known as hierarchical phosphorylation. Therefore, the proteasome inhibition might result in an increase in the levels of all 3 phosphorylated TH forms, thus complicating interpretation of data. Conversely, activation of proteasome degradation by IU-1, which is an inhibitor for the deubiquitinating activity of USP14, decreased only the quantity of TH molecules phosphorylated at their Ser19, although it did not decrease that of TH phosphorylated at its Ser31 and Ser40 or that of TH molecules. These results suggest that the phosphorylation of Ser19 in the N-terminal portion of TH is critical as a trigger for the degradation of this enzyme by the ubiquitin-proteasome pathway.

Melatonin and ubiquitin: what's the connection?

Melatonin has been widely studied for its role in photoperiodism in seasonal breeders; it is also a potent antioxidant. Ubiquitin, a protein also widespread in living cells, contributes to many cellular events, although the most well known is that of tagging proteins for destruction by the proteasome. Herein, we suggest a model in which melatonin interacts with the ubiquitin-proteasome system to regulate a variety of seemingly unrelated processes. Ubiquitin, for example, is a major regulator of central activity of thyroid hormone type 2 deiodinase; the subsequent regulation of T3 may be central to the melatonin-induced changes in seasonal reproduction and seasonal changes in metabolism. Both melatonin and ubiquitin also have important roles in protecting cells from oxidative stress. We discuss the interaction of melatonin and the ubiquitin-proteasome system in oxidative stress through regulation of the ubiquitin-activating enzyme, E1. Previous reports have shown that glutathiolation of this enzyme protects proteins from unnecessary degradation. In addition, evidence is discussed concerning the interaction of ubiquitin and melatonin in activation of the transcription factor NF-κB as well as modulating cellular levels of numerous signal transducing factors including the tumor suppressor, p53. Some of the actions of melatonin on the regulatory particle of the proteasome appear to be related to its inhibition of the calcium-dependent calmodulin kinase II, an enzyme which reportedly copurifies with proteasomes. Many of the actions of melatonin on signal transduction are similar to those of a proteasome inhibitor. While these actions of melatonin could be explained by a direct inhibitory action on the catalytic core particle of the proteasome, this has not been experimentally verified. If our hypothesis of melatonin as a general inhibitor of the ubiquitin-proteasome system is confirmed, it is predicted that more examples of this interaction will be demonstrated in a variety of tissues in which ubiquitin and melatonin co-exist. Furthermore, the hypothesis of melatonin as an inhibitor of the ubiquitin-proteasome system will be a very useful model for clinical testing of melatonin.

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.

ser31 Tyrosine hydroxylase phosphorylation parallels differences in dopamine recovery in nigrostriatal pathway following 6-OHDA lesion

Compensatory mechanisms in dopamine (DA) signaling have long been proposed to delay onset of locomotor symptoms during Parkinson's disease progression until ~ 80% loss of striatal DA occurs. Increased striatal dopamine turnover has been proposed to be a part of this compensatory response, but may occur after locomotor symptoms. Increased tyrosine hydroxylase (TH) activity has also been proposed as a mechanism, but the impact of TH protein loss upon site-specific TH phosphorylation in conjunction with the impact on DA tissue content is not known. The tissue content of DA was determined against TH protein loss in the striatum and substantia nigra (SN) following 6-hydroxydopamine lesion in the medial forebrain bundle in young Sprague-Dawley male rats. Although DA predictably decreased in both regions following 6-hydroxydopamine, there was a significant difference in DA loss between the striatum (75%) and SN (40%), despite similar TH protein loss. Paradoxically, there was a significant decrease in DA against remaining TH protein in striatum, but a significant increase in DA against remaining TH in SN. In the SN, increased DA per remaining TH protein was matched by increased ser31, but not ser40, TH phosphorylation. In striatum, both ser31 and ser40 phosphorylation decreased, reflecting decreased DA per TH. However, in control nigral and striatal tissue, only ser31 phosphorylation correlated with DA per TH protein. Combined, these results suggest that the phosphorylation of ser31 in the SN may be a mechanism to increase DA biosynthesis against TH protein loss in an in vivo model of Parkinson's disease. Properties of dopamine biosynthesis were evaluated in the 6-OHDA model of Parkinson's disease by studying the impact of tyrosine hydroxylase (TH) protein loss on its own phosphorylation and dopamine (DA) tissue content in rat nigrostriatal pathway. A dichotomous response was observed between striatum and substantia nigra in that dopamine per remaining TH decreased in striatum, but increased in substantia nigra. Phosphorylation at ser31 reflected these differences, indicating that ser31 phosphorylation may be critical to maintain dopamine with progressive TH protein loss. Drawings are from slides purchased from Motifolio (http://motifolio.com/).

Chronic L-DOPA treatment attenuates behavioral and biochemical deficits induced by unilateral lactacystin administration into the rat substantia nigra

The aim of the study was to determine whether the dopamine (DA) precursor l-DOPA attenuates parkinsonian-like symptoms produced by the ubiquitin-proteasome system inhibitor lactacystin. Wistar rats were injected unilaterally with lactacystin (2.5 μg/2 μl) or 6-OHDA (8 μg/2 μl) into the substantia nigra (SN) pars compacta. Four weeks after the lesion, the animals were treated chronically with l-DOPA (25 or 50 mg/kg) for two weeks. During l-DOPA treatment, the lactacystin-treated rats were tested for catalepsy and forelimb asymmetry. Rotational behavior was evaluated after apomorphine (0.25 mg/kg) and l-DOPA in both PD models. After completion of experiments, the animals were killed and the levels of DA and its metabolites in the striatum and SN were assayed. We found that acute l-DOPA administration effectively decreased catalepsy and increased the use of the compromised forelimb in the cylinder test. However, the lactacystin group did not respond to apomorphine or acute l-DOPA administration in the rotational test. Repeated l-DOPA treatment produced contralateral rotations in both PD models, but the number of rotations was much greater in the 6-OHDA-lesioned rats. Both toxins markedly (>90%) reduced the levels of DA and its metabolites in the striatum and SN, while l-DOPA diminished these decreases, especially in the SN. By demonstrating the efficacy of l-DOPA in several behavioral tests, our study confirms the usefulness of the lactacystin lesion as a model of PD. However, marked differences in the rotational response to apomorphine and l-DOPA suggest different mechanisms of neurodegeneration evoked by lactacystin and 6-OHDA.