Effects of Xylanase A double mutation on substrate specificity and structural dynamics.

While protein activity is traditionally studied with a major focus on the active site, the activity of enzymes has been hypothesized to be linked to the flexibility of adjacent regions, warranting more exploration into how the dynamics in these regions affects catalytic turnover. One such enzyme is Xylanase A (XylA), which cleaves hemicellulose xylan polymers by hydrolysis at internal ß-1,4-xylosidic linkages. It contains a "thumb" region whose flexibility has been suggested to affect the activity. The double mutation D11F/R122D was previously found to affect activity and potentially bias the thumb region to a more open conformation. We find that the D11F/R122D double mutation shows substrate-dependent effects, increasing activity on the non-native substrate ONPX2 but decreasing activity on its native xylan substrate. To characterize how the double mutant causes these kinetics changes, nuclear magnetic resonance (NMR) and molecular dynamics (MD) simulations were used to probe structural and flexibility changes. NMR chemical shift perturbations revealed structural changes in the double mutant relative to the wild-type, specifically in the thumb and fingers regions. Increased slow-timescale dynamics in the fingers region was observed as intermediate-exchange line broadening. Lipari-Szabo order parameters show negligible changes in flexibility in the thumb region in the presence of the double mutation. To help understand if there is increased energetic accessibility to the open state upon mutation, alchemical free energy simulations were employed that indicated thumb opening is more favorable in the double mutant. These studies aid in further characterizing how flexibility in adjacent regions affects the function of XylA.

In Vitro and In Silico Explorations of the Protein Conformational Changes of Corynebacterium glutamicum MshA, a Model Retaining GT-B Glycosyltransferase.

MshA is a GT-B glycosyltransferase catalyzing the first step in the biosynthesis of mycothiol. While many GT-B enzymes undergo an open-to-closed transition, MshA is unique because its 97° rotation is beyond the usual range of 10-25°. Molecular dynamics (MD) simulations were carried out for MshA in both ligand bound and unbound states to investigate the effect of ligand binding on localized protein dynamics and its conformational free energy landscape. Simulations showed that both the unliganded "opened" and liganded "closed" forms of the enzyme sample a wide degree of dihedral angles and interdomain distances with relatively low overlapping populations. Calculation of the free energy surface using replica exchange MD for the apo "opened" and an artificial generated apo "closed" structure revealed overlaps in the geometries sampled, allowing calculation of a barrier of 2 kcal/mol for the open-to-closed transition in the absence of ligands. MD simulations of fully liganded MshA revealed a smaller sampling of the dihedral angles. The localized protein fluctuation changes suggest that UDP-GlcNAc binding activates the motions of loops in the 1-l-myo-inositol-1-phosphate (I1P)-binding site despite little change in the interactions with UDP-GlcNAc. Circular dichroism, intrinsic fluorescence spectroscopy, and mutagenesis studies were used to confirm the ligand-induced structural changes in MshA. The results support a proposed mechanism where UDP-GlcNAc binds with rigid interactions to the C-terminal domain of MshA and activates flexible loops in the N-terminal domain for binding and positioning of I1P. This model can be used for future structure-based drug development of inhibitors of the mycothiol biosynthetic pathway.

How Single Amino Acid Substitutions Can Disrupt a Protein Hetero-Dimer Interface: Computational and Experimental Studies of the LigAB Dioxygenase from Sphingobium sp. Strain SYK-6.

Protocatechuate 4,5-dioxygenase (LigAB) is a heterodimeric enzyme that catalyzes the dioxygenation of multiple lignin derived aromatic compounds. The active site of LigAB is at the heterodimeric interface, with specificity conferred by the alpha subunit and catalytic residues contributed by the beta subunit. Previous research has indicated that the phenylalanine at the 103 position of the alpha subunit (F103α) controls selectivity for the C5 position of the aromatic substrates, and mutations of this residue can enhance the rate of catalysis for substrates with larger functional groups at this position. While several of the mutations to this position (Valine, V; Threonine, T; Leucine, L; and Histidine, H) were catalytically active, other mutations (Alanine, A; and Serine, S) were found to have reduced dimer interface affinity, leading to challenges in copurifing the catalytically active enzyme complex under high salt conditions. In this study, we aimed to experimentally and computationally interrogate residues at the dimer interface to discern the importance of position 103α for maintaining the integrity of the heterodimer. Molecular dynamic simulations and electrophoretic mobility assays revealed a preference for nonpolar/aromatic amino acids in this position, suggesting that while substitutions to polar amino acids may produce a dioxygenase with a useful substrate utilization profile, those considerations may be off-set by potential destabilization of the catalytically active oligomer. Understanding the dimerization of LigAB provides insight into the multimeric proteins within the largely uncharacterized superfamily and characteristics to consider when engineering proteins that can degrade lignin efficiently. These results shed light on the challenges associated with engineering proteins for broader substrate specificity.

Kinetic Characterization and Computational Modeling of Escherichia coli Heptosyltransferase II: Exploring the Role of Protein Dynamics in Catalysis for GT-B Glycosyltransferase.

Glycosyltransferase (GT) enzymes promote the formation of glycosidic bonds between a sugar molecule and a diversity of substrates. Heptosyltransferase II (HepII) is a GT involved in the lipopolysaccharide (LPS) biosynthetic pathway that transfers the seven-carbon sugar (l-glycero-d-manno-heptose, Hep) onto a lipid-anchored glycopolymer (heptosylated Kdo2-Lipid A, Hep-Kdo2-Lipid A, or HLA). LPS plays a key role in Gram-negative bacterial sepsis, biofilm formation, and host colonization, and as such, LPS biosynthetic enzymes are targets for novel antimicrobial therapeutics. Three heptosyltransferases are involved in the inner-core LPS biosynthesis, with Escherichia coli HepII being the last to be quantitatively characterized in vivo. HepII shares modest sequence similarity with heptosyltransferase I (HepI) while maintaining a high degree of structural homology. Here, we report the first kinetic and biophysical characterization of HepII and demonstrate the properties of HepII that are shared with HepI, including sugar donor promiscuity and sugar acceptor-induced secondary structural changes, which results in significant thermal stabilization. HepII also has an increased catalytic efficiency and a significantly tighter binding affinity for both of its substrates compared to HepI. A structural model of the HepII ternary complex, refined by molecular dynamics simulations, was developed to probe the potentially important substrate-protein contacts. Ligand binding-induced changes in Trp fluorescence in HepII enabled the determination of substrate dissociation constants. Combined, these efforts meaningfully enhance our understanding of the heptosyltransferase family of enzymes and will aid in future efforts to design novel, potent, and specific inhibitors for this family of enzymes.

Discovery of first-in-class nanomolar inhibitors of heptosyltransferase I reveals a new aminoglycoside target and potential alternative mechanism of action.

A clinically relevant inhibitor for Heptosyltransferase I (HepI) has been sought after for many years because of its critical role in the biosynthesis of lipopolysaccharides on bacterial cell surfaces. While many labs have discovered or designed novel small molecule inhibitors, these compounds lacked the bioavailability and potency necessary for therapeutic use. Extensive characterization of the HepI protein has provided valuable insight into the dynamic motions necessary for catalysis that could be targeted for inhibition. Structural inspection of Kdo2-lipid A suggested aminoglycoside antibiotics as potential inhibitors for HepI. Multiple aminoglycosides have been experimentally validated to be first-in-class nanomolar inhibitors of HepI, with the best inhibitor demonstrating a Ki of 600 ± 90 nM. Detailed kinetic analyses were performed to determine the mechanism of inhibition while circular dichroism spectroscopy, intrinsic tryptophan fluorescence, docking, and molecular dynamics simulations were used to corroborate kinetic experimental findings. While aminoglycosides have long been described as potent antibiotics targeting bacterial ribosomes' protein synthesis leading to disruption of the stability of bacterial cell membranes, more recently researchers have shown that they only modestly impact protein production. Our research suggests an alternative and novel mechanism of action of aminoglycosides in the inhibition of HepI, which directly leads to modification of LPS production in vivo. This finding could change our understanding of how aminoglycoside antibiotics function, with interruption of LPS biosynthesis being an additional and important mechanism of aminoglycoside action. Further research to discern the microbiological impact of aminoglycosides on cells is warranted, as inhibition of the ribosome may not be the sole and primary mechanism of action. The inhibition of HepI by aminoglycosides may dramatically alter strategies to modify the structure of aminoglycosides to improve the efficacy in fighting bacterial infections.

Cytochromes P450: Role in Carcinogenesis and Relevance to Cancers.

Cancer is a leading cause of mortality globally. Cytochrome P450 (CYP) enzymes play a pivotal role in the biotransformation of both endogenous and exogenous compounds. Various lines of evidence from epidemiological, animal, and clinical studies point to the instrumental role of CYPs in cancer initiation, metastasis, and prevention. Substantial research has found that CYPs are involved in activating different carcinogenic chemicals in the environment, such as polycyclic aromatic hydrocarbons and tobacco-related nitrosamines. Electrophilic intermediates produced from these chemicals can covalently bind to DNA, inducing mutation and cellular transformation that collectively result in cancer development. While bioactivation of procarcinogens and promutagens by CYPs has long been established, the role of CYP-derived endobiotics in carcinogenesis has only emerged in recent years. Eicosanoids derived from arachidonic acid via CYP oxidative pathways have been implicated in tumorigenesis, cancer progression and metastasis. The purpose of this review is to update the current state of knowledge about the molecular cancer mechanism involving CYPs with a focus on the biochemical and biotransformation mechanisms in the various CYP-mediated carcinogenesis and the role of CYP-derived reactive metabolites, from both external and endogenous sources, in cancer growth and tumor formation.

Ligand-Induced Conformational and Dynamical Changes in a GT-B Glycosyltransferase: Molecular Dynamics Simulations of Heptosyltransferase I Complexes.

Understanding the dynamical motions and ligand recognition motifs of heptosyltransferase I (HepI) can be critical to discerning the behavior of other glycosyltransferase (GT) enzymes. Prior studies in our lab have demonstrated that GTs in the GT-B structural class, which are characterized by their connection of two Rossman-like domains by a linker region, have conserved structural fold and dynamical motions, despite low sequence homology, therefore making discoveries found in HepI transferable to other GT-B enzymes. Through molecular dynamics simulations and ligand binding free energy analysis of HepI in the apo and bound complexes (for all kinetically relevant combinations of the native substrates/products), we have determined the energetically favored enzymatic pathway for ligand binding and release. Our principal component, dynamic cross correlation, and network analyses of the simulations have revealed correlated motions involving residues within the N-terminal domain communicating with C-terminal domain residues via both proximal amino acid residues and also functional groups of the bound substrates. Analyses of the structural changes, energetics of substrate/product binding, and changes in pKa have elucidated a variety of inter and intradomain interactions that are critical for enzyme catalysis. These data corroborate our experimental observations of protein conformational changes observed in both presteady state kinetic and circular dichroism analyses of HepI. These simulations provided invaluable structural insights into the regions involved in HepI conformational rearrangement upon ligand binding. Understanding the specific interactions governing conformational changes is likely to enhance our efforts to develop novel dynamics disrupting inhibitors against GT-B structural enzymes in the future.

Insights from molecular docking and molecular dynamics on the potential of vitexin as an antagonist candidate against lipopolysaccharide (LPS) for microglial activation in neuroinflammation.

BACKGROUND: Neuroinflammation has been identified to be the key player in most neurodegenerative diseases. If neuroinflammation is left to be unresolved, chronic neuroinflammation will be establish. Such situation is due to the overly-activated microglia which have the tendency to secrete an abundance amount of pro-inflammatory cytokines into the neuron microenvironment. The abundance of pro-inflammatory cytokines will later cause toxic and death to neurons. Toll-like receptor 4 (TLR4)/MD-2 complex found on the cell surface of microglia is responsible for the attachment of LPS and activation of nuclear factor-κB (NF-κB) downstream signalling pathway. Albeit vitexin has been shown to possess anti-inflammatory property, however, little is known on its ability to bind at the binding site of TLR4/MD-2 complex of microglia as well as to be an antagonist for LPS. RESULTS: The present study reveals that both vitexin and donepezil are able to bind at the close proximity of LPS binding site located at the TLR4/MD-2 complex with the binding energy of - 4.35 and - 9.14 kcal/mol, respectively. During molecular dynamic simulations, both vitexin and donepezil formed stable complex with TLR4/MD-2 throughout the 100 ns time length with the root mean square deviation (RMSD) values of 2.5 Å and 4.0 Å, respectively. The root mean square fluctuation (RMSF) reveals that both compounds are stable. Interestingly, the radius of gyration (rGyr) for donepezil shows notable fluctuations when compare with vitexin. The MM-GBSA results showed that vitexin has higher binding energy in comparison with donepezil. CONCLUSIONS: Taken together, the findings suggest that vitexin is able to bind at the binding site of TLR4/MD-2 complex with more stability than donepezil throughout the course of 100 ns simulation. Hence, vitexin has the potential to be an antagonist candidate for LPS.

Conserved Conformational Hierarchy across Functionally Divergent Glycosyltransferases of the GT-B Structural Superfamily as Determined from Microsecond Molecular Dynamics.

It has long been understood that some proteins undergo conformational transitions en route to the Michaelis Complex to allow chemistry. Examination of crystal structures of glycosyltransferase enzymes in the GT-B structural class reveals that the presence of ligand in the active site triggers an open-to-closed conformation transition, necessary for their catalytic functions. Herein, we describe microsecond molecular dynamics simulations of two distantly related glycosyltransferases that are part of the GT-B structural superfamily, HepI and GtfA. Simulations were performed using the open and closed conformations of these unbound proteins, respectively, and we sought to identify the major dynamical modes and communication networks that interconnect the open and closed structures. We provide the first reported evidence within the scope of our simulation parameters that the interconversion between open and closed conformations is a hierarchical multistep process which can be a conserved feature of enzymes of the same structural superfamily. Each of these motions involves of a collection of smaller molecular reorientations distributed across both domains, highlighting the complexities of protein dynamic involved in the interconversion process. Additionally, dynamic cross-correlation analysis was employed to explore the potential effect of distal residues on the catalytic efficiency of HepI. Multiple distal nonionizable residues of the C-terminal domain exhibit motions anticorrelated to positively charged residues in the active site in the N-terminal domain involved in substrate binding. Mutations of these residues resulted in a reduction in negatively correlated motions and an altered enzymatic efficiency that is dominated by lower Km values with kcat effectively unchanged. The findings suggest that residues with opposing conformational motions involved in the opening and closing of the bidomain HepI protein can allosterically alter the population and conformation of the "closed" state, essential to the formation of the Michaelis complex. The stabilization effects of these mutations likely equally influence the energetics of both the ground state and the transition state of the catalytic reaction, leading to the unaltered kcat. Our study provides new insights into the role of conformational dynamics in glycosyltransferase's function and new modality to modulate enzymatic efficiency.

Concurrent stroke and ST-elevation myocardial infarction: Is it a contraindication for intravenous tenecteplase?

Acute ischemic stroke (AIS) and acute ST-elevation myocardial infarction (STEMI) are leading causes of mortality worldwide. Concurrent AIS presentation with STEMI is rare and potentially fatal. Most importantly to date many centres in Malaysia are still not aware on how to treat this condition. We report a case of AIS, which was treated with intravenous tenecteplase (TNK) according to ischemic stroke dosage and lead to improvement of neurological deficit.

A systematic review of contemporary management of oligometastatic prostate cancer: fighting a challenge or tilting at windmills?

PURPOSE: Amongst the unanswered questions regarding prostate cancer (PCa), the optimal management of oligometastatic disease remains one of the major concerns of the scientific community. The very existence of this category is still subject to controversy. Aim of this systematic review is to summarize current available data on the most appropriate management of oligometastatic PCa. EVIDENCE ACQUISITION: All relevant studies published in English up to November the 1st were identified through systematic searches in PubMed, EMBASE, Cochrane Library, CINAHL, Google Scholar and Ovid database. A search was performed including the combination of following words: (prostate cancer) and (metastatic) and [(oligo) or (PSMA) or (cytoreductive) or (stereotaxic radiotherapy) or (prostatectomy)]. 3335 articles were reviewed. After title screening and abstract reading, 118 papers were considered for full reading, leaving a total of 36 articles for the systematic review. EVIDENCE SYNTHESIS: There is still no consensus on the definition of oligometastatic disease, nor on the imaging modalities used for its detection. While retrospective studies suggest an added benefit with the treatment the primitive tumor by cytoreductive prostatectomy (55% survival rate vs 21%, p < 0.001), prospective studies do not validate the same outcome. Nonetheless, most studies have reported a reduction in local complications after cytoreductive prostatectomy (< 10%) compared to the best systemic treatment (25-30%). Concerning radiotherapy, an overall survival benefit for patients with a low metastatic burden was found in STAMPEDE (HR 0.68, 95% CI 0.52-0.90; p = 0.007) and suggested in subgroup analysis of the HORRAD trial. Regarding the impact of metastases-directed therapy (MDT), the STOMP and ORIOLE trials suggested that metastatic disease control might improve androgen deprivation therapy-free survival (in STOMP: 21 vs 13 months for MDT vs standard of care). Nonetheless, the impact of MDT on long-term oncologic results remains unclear. Finally, oligometastatic disease appears to be a biologically different entity compared to high-burden metastatic disease. New findings on exosomes appear to make them intriguing biomarkers in the early phases of oligometastatic PCa. CONCLUSION: Oligometastatic PCa is today a poorly understood disease. The implementation of new imaging techniques as whole-body MRI and PSMA PET/CT has increased exponentially the number of oligometastatic patients detected. Data of available trials suggest a benefit from cytoreductive prostatectomy to reduce local complication, though its impact on survival remains unknown. Radiotherapy may be beneficial for patients with low-burden metastatic PCa, while MDT may delay the need for androgen deprivation therapy. Results from ongoing trials data are eagerly awaited to draw reliable recommendations.

Down-regulation of steroidogenesis-related genes and its accompanying fertility decline in streptozotocin-induced diabetic male rats: ameliorative effect of metformin.

BACKGROUND: Metformin has long been used for glycemic control in diabetic state. Recently, other benefits of metformin beyond blood glucose regulation have emerged. OBJECTIVES: To investigate the effect of metformin on the expression of testicular steroidogenesis-related genes, spermatogenesis, and fertility of male diabetic rats. MATERIALS AND METHODS: Eighteen adult male Sprague Dawley rats were divided into three groups, namely normal control (NC), diabetic control (DC), and metformin-treated (300 mg/kg body weight/day) diabetic rats (D+Met). Diabetes was induced using a single intraperitoneal injection of streptozotocin (60 mg/kg b.w.), followed by oral treatment with metformin for four weeks. RESULTS: Diabetes decreased serum and intratesticular testosterone levels and increased serum but not intratesticular levels of luteinizing hormone. Sperm count, motility, viability, and normal morphology were decreased, while sperm nuclear DNA fragmentation was increased in DC group, relative to NC group. Testicular mRNA levels of androgen receptor, luteinizing hormone receptor, cytochrome P450 enzyme (CYP11A1), steroidogenic acute regulatory (StAR) protein, 3ß-hydroxysteroid dehydrogenase (HSD), and 17ß-HSD, as well as the level of StAR protein and activities of CYP11A1, 3ß-HSD, and 17ß-HSD, were decreased in DC group. Similarly, decreased activities of epididymal antioxidant enzymes and increased lipid peroxidation were observed in DC group. Consequently, decreased litter size, fetal weight, mating and fertility indices, and increased pre- and post-implantation losses were recorded in DC group. Following intervention with metformin, we observed increases in serum and intratesticular testosterone levels, Leydig cell count, improved sperm parameters, and decreased sperm nuclear DNA fragmentation. Furthermore, mRNA levels and activities of steroidogenesis-related enzymes were increased, with improved fertility outcome. DISCUSSION AND CONCLUSION: Diabetes mellitus is associated with dysregulation of steroidogenesis, abnormal spermatogenesis, and fertility decline. Controlling hyperglycemia is therefore crucial in preserving male reproductive function. Metformin not only regulates blood glucose level, but also preserves male fertility in diabetic state.

Cyp2a5 Promoter-based Gene Reporter Assay: A Novel Design of Cell-based Bioassay for Toxicity Prediction.

The murine cytochrome P450 2a5 (Cyp2a5) gene is regulated by complex interactions of various stress-activated transcription factors (TFs). Elevated Cyp2a5 transcription under chemical-induced stress conditions is achieved by interplay between the various TFs - including as aryl hydrocarbon receptor (AhR) and nuclear factor (erythroid-derived 2)-like 2 wild-type (Nrf2) - at the 'stress-responding' cluster of response elements on the Cyp2a5 promoter, as well as through mRNA stabilization mediated by interaction of the stress-activated heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) with the 3'-UTR of the CYP2A5 mRNA. We designed a unique toxicity pathway-based reporter assay to include regulatory regions from both the 5' and the 3' untranslated regions of Cyp2a5 in a luciferase reporter plasmid to reflect in vivo responses to chemical insult. Human breast cancer MCF-7 cells were stably transfected with pGL4.38-Cyp2a5_Wt3k (wild-type) or mutant - pGL4.38-Cyp2a5_StREMut and pGL4.38-Cyp2a5_XREMut - reporter gene to monitor chemical-induced cellular response mediated by AhR and Nrf2 signalling. The recombinant cells were treated with representative of AhR agonist, polycyclic aromatic hydrocarbons, brominated flame retardant, fluorosurfactant, aromatic organic compound and metal, to determine the sensitivity of the Cyp2a5 promoter-based gene reporter assays to chemical insults by measuring the LC50 and EC50 of the respective chemicals. The three assays are sensitive to sublethal cellular responses of chemicals, which is an ideal feature for toxicity pathway-based bioassay for toxicity prediction. The wild-type reporter responded well to chemicals that activate crosstalk between the AhR and Nrf2, whilst the mutant reporters effectively gauge cellular response driven by either Nrf2/StRE or AhR/XRE signalling. Thus, the three gene reporter assays could be used tandemly to determine the predominant toxicity pathway of a given compound.

A clinical audit of interventional pain procedures performed as part of the newly initiated pain service in a local neurosurgical centre.

Interventional Pain Procedures (IPPs) is a relatively new treatment modality for chronic pain in Malaysia. The Interventional Pain Service (IPS) newly set up in our institution is led by a pain neurosurgeon and provides a whole package of multimodal pain management including different range of IPPs. This clinical audit is to examine the quality of IPPs performed within the IPS in our institution since its initiation. A total of 87 IPPs were performed on 56 chronic pain patients over 3-year duration. As high as 81.8% of the procedures were effective and 81.5% of patients were satisfied. Only one minor transient complication occurred after an intradiscal procedure but none resulted in death or permanent disability. Thus, safe and effective IPPs can be provided as part of IPS in a local neurosurgical pain centre to bring more comprehensive and less fragmented care for chronic pain patients.

Tumour suppressor protein p53 regulates the stress activated bilirubin oxidase cytochrome P450 2A6.

Human cytochrome P450 (CYP) 2A6 enzyme has been proposed to play a role in cellular defence against chemical-induced oxidative stress. The encoding gene is regulated by various stress activated transcription factors. This paper demonstrates that p53 is a novel transcriptional regulator of the gene. Sequence analysis of the CYP2A6 promoter revealed six putative p53 binding sites in a 3kb proximate promoter region. The site closest to transcription start site (TSS) is highly homologous with the p53 consensus sequence. Transfection with various stepwise deletions of CYP2A6-5'-Luc constructs--down to -160bp from the TSS--showed p53 responsiveness in p53 overexpressed C3A cells. However, a further deletion from -160 to -74bp, including the putative p53 binding site, totally abolished the p53 responsiveness. Electrophoretic mobility shift assay with a probe containing the putative binding site showed specific binding of p53. A point mutation at the binding site abolished both the binding and responsiveness of the recombinant gene to p53. Up-regulation of the endogenous p53 with benzo[α]pyrene--a well-known p53 activator--increased the expression of the p53 responsive positive control and the CYP2A6-5'-Luc construct containing the intact p53 binding site but not the mutated CYP2A6-5'-Luc construct. Finally, inducibility of the native CYP2A6 gene by benzo[α]pyrene was demonstrated by dose-dependent increases in CYP2A6 mRNA and protein levels along with increased p53 levels in the nucleus. Collectively, the results indicate that p53 protein is a regulator of the CYP2A6 gene in C3A cells and further support the putative cytoprotective role of CYP2A6.

Zinc: indications in brain disorders.

Zinc is the authoritative metal which is present in our body, and reactive zinc metal is crucial for neuronal signaling and is largely distributed within presynaptic vesicles. Zinc also plays an important role in synaptic function. At cellular level, zinc is a modulator of synaptic activity and neuronal plasticity in both development and adulthood. Different importers and transporters are involved in zinc homeostasis. ZnT-3 is a main transporter involved in zinc homeostasis in the brain. It has been found that alterations in brain zinc status have been implicated in a wide range of neurological disorders including impaired brain development and many neurodegenerative disorders such as Alzheimer's disease, and mood disorders including depression, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and prion disease. Furthermore, zinc has also been implicated in neuronal damage associated with traumatic brain injury, stroke, and seizure. Understanding the mechanisms that control brain zinc homeostasis is thus critical to the development of preventive and treatment strategies for these and other neurological disorders.

Mitochondrial targeting of bilirubin regulatory enzymes: An adaptive response to oxidative stress.

The intracellular level of bilirubin (BR), an endogenous antioxidant that is cytotoxic at high concentrations, is tightly controlled within the optimal therapeutic range. We have recently described a concerted intracellular BR regulation by two microsomal enzymes: heme oxygenase 1 (HMOX1), essential for BR production and cytochrome P450 2A5 (CYP2A5), a BR oxidase. Herein, we describe targeting of these enzymes to hepatic mitochondria during oxidative stress. The kinetics of microsomal and mitochondrial BR oxidation were compared. Treatment of DBA/2J mice with 200mgpyrazole/kg/day for 3days increased hepatic intracellular protein carbonyl content and induced nucleo-translocation of Nrf2. HMOX1 and CYP2A5 proteins and activities were elevated in microsomes and mitoplasts but not the UGT1A1, a catalyst of BR glucuronidation. A CYP2A5 antibody inhibited 75% of microsomal BR oxidation. The inhibition was absent in control mitoplasts but elevated to 50% after treatment. An adrenodoxin reductase antibody did not inhibit microsomal BR oxidation but inhibited 50% of mitochondrial BR oxidation. Ascorbic acid inhibited 5% and 22% of the reaction in control and treated microsomes, respectively. In control mitoplasts the inhibition was 100%, which was reduced to 50% after treatment. Bilirubin affinity to mitochondrial and microsomal CYP2A5 enzyme is equally high. Lastly, the treatment neither released cytochrome c into cytoplasm nor dissipated membrane potential, indicating the absence of mitochondrial membrane damage. Collectively, the observations suggest that BR regulatory enzymes are recruited to mitochondria during oxidative stress and BR oxidation by mitochondrial CYP2A5 is supported by mitochondrial mono-oxygenase system. The induced recruitment potentially confers membrane protection.

Job satisfaction and perceived future roles of Malaysian dental therapists: findings from a national survey.

OBJECTIVE: To assess Malaysian dental therapists' perceptions of their job satisfaction and future roles. METHODS: A nationwide postal survey involving all Malaysian dental therapists who met the inclusion criteria (n = 1726). RESULTS: The response rate was 76.8%. All respondents were females; mean age 35.4 years (SD = 8.4). Majority were married (85.5%) and more than one-half had a working experience of <10 years (56.1%). Majority worked in community dental service (94.3%) and in urban areas (61.7%). Overall, they were highly satisfied with most aspects of their career. However, they were least satisfied with administrative workload (58.1%), career advancement opportunities (51.9%) and remuneration package; specifically income (45.2%), allowances (45.2%) and non-commensurate between pay and performance (44.0%). Majority perceived their role as very important in routine clinical tasks such as examination and diagnosis, preventive treatment, extraction of deciduous teeth and oral health promotion. However, fewer than one-half consider complex treatment such as placement of preformed crowns on deciduous teeth (37.1%) and extraction of permanent teeth (37.2%) as very important tasks. CONCLUSION: Majority expressed high career satisfaction with most aspects of their employment but expressed low satisfaction in remuneration, lack of career advancement opportunities and administrative tasks. We conclude that most Malaysian dental therapists have positive perceptions of their current roles but do not favour wider expansion of their roles. These findings imply that there was a need to develop a more attractive career pathway for therapists to ensure sustainability of effective primary oral healthcare delivery system for Malaysia's children.

Solving self-mixing equations for arbitrary feedback levels: a concise algorithm.

Self-mixing laser sensors show promise for a wide range of sensing applications, including displacement, velocimetry, and fluid flow measurements. Several techniques have been developed to simulate self-mixing signals; however, a complete and succinct process for synthesizing self-mixing signals has so far been absent in the open literature. This article provides a systematic numerical approach for the analysis of self-mixing sensors using the steady-state solution to the Lang and Kobayashi model. Examples are given to show how this method can be used to synthesize self-mixing signals for arbitrary feedback levels and for displacement, distance, and velocity measurement. We examine these applications with a deterministic stimulus and discuss the velocity measurement of a rough surface, which necessitates the inclusion of a random stimulus.