The ability of cobalamin to coordinate different upper axial ligands gives rise to a diversity of reactivity. Traditionally, adenosylcobalamin is associated with radical-based rearrangements, and methylcobalamin with methyl cation transfers. Recently, however, a new role for adenosylcobalamin has been discovered as a light sensor, and a methylcobalamin-dependent enzyme has been identified that is suggested to transfer a methyl anion. Additionally, recent studies have provided a wealth of new information about a third class of cobalamin-dependent enzymes that do not appear to use an upper ligand. They function in reductive dehalogenations and epoxide reduction reactions. Finally, mechanistic details are beginning to emerge about the cobalamin-dependent -adenosylmethionine radical enzyme superfamily for which the role of cobalamin has been largely enigmatic.
The voltage-gated K 1.3 channel in T lymphocytes is a validated therapeutic target for diverse autoimmune diseases. Here we review the discovery of K 1.3, its physiological role in T cells, and why it is an attractive target for modulating autoimmune responses. We focus on peptide inhibitors because the first K 1.3-selective inhibitor in human trials is a peptide derived from a marine organism. Two broad classes of peptides block K 1.3, the first from scorpions and the second from sea anemones. We describe their structures, their binding site in the external vestibule of K 1.3, how they have been engineered to improve K 1.3-specificity, and their pharmacokinetic and pharmacodynamic properties. Finally, we highlight the therapeutic potential of K 1.3 peptide inhibitors to treat autoimmune diseases without compromising protective immune responses.
The biological activity and structural diversity of natural products are unsurpassed by any available synthetic screening libraries. As such, these privileged scaffolds serve as important, biologically prevalidated platforms for the design of compound libraries in the search for new drug candidates. Recent progress has focussed on improving the potency, selectivity and pharmacokinetics of bioactive natural products through structural modification, leading to the emergence of a number of drug-like lead compounds. Here, we review recent advances in the exploitation of terpenoid, polyketide, phenylpropanoid and alkaloid natural product scaffolds for inspiration in the design and development of important new drug candidates.
Cholinergic regulation of dopaminergic inputs into the striatum is critical for normal basal ganglia (BG) function. This regulation of BG function is thought to be primarily mediated by acetylcholine released from cholinergic interneurons (ChIs) acting locally in the striatum. We now report a combination of pharmacological, electrophysiological, optogenetic, chemogenetic, and functional magnetic resonance imaging studies suggesting extra-striatal cholinergic projections from the pedunculopontine nucleus to the substantia nigra pars reticulata (SNr) act on muscarinic acetylcholine receptor subtype 4 (M ) to oppose cAMP-dependent dopamine receptor subtype 1 (D ) signaling in presynaptic terminals of direct pathway striatal spiny projections neurons. This induces a tonic inhibition of transmission at direct pathway synapses and D -mediated activation of motor activity. These studies provide important new insights into the unique role of M in regulating BG function and challenge the prevailing hypothesis of the centrality of striatal ChIs in opposing dopamine regulation of BG output. Moehle et al. show activation of M can induce inhibition of D signaling. Interestingly, this mechanism occurs on direct pathway terminals in the SNr from acetylcholine released by hindbrain cholinergic projections, expanding the model of cholinergic regulation of the BG.
N6-methyladenosine (m6A) constitutes one of the most abundant internal RNA modifications and is critical for RNA metabolism and function. It has been previously reported that viral RNA contains internal m6A modifications; however, only recently the function of m6A modification in viral RNAs has been elucidated during infections of HIV, hepatitis C virus and Zika virus. In the present study, we found that enterovirus 71 (EV71) RNA undergoes m6A modification during viral infection, which alters the expression and localization of the methyltransferase and demethylase of m6A, and its binding proteins. Moreover, knockdown of m6A methyltransferase resulted in decreased EV71 replication, whereas knockdown of the demethylase had the opposite effect. Further study showed that the m6A binding proteins also participate in the regulation of viral replication. In particular, two m6A modification sites were identified in the viral genome, of which mutations resulted in decreased virus replication, suggesting that m6A modification plays an important role in EV71 replication. Notably, we found that METTL3 interacted with viral RNA-dependent RNA polymerase 3D and induced enhanced sumoylation and ubiquitination of the 3D polymerase that boosted viral replication. Taken together, our findings demonstrated that the host m6A modification complex interacts with viral proteins to modulate EV71 replication.
Schizophrenia is one of the leading causes of disability among mental disorders, contributing to a substantial socioeconomic burden. Our understanding of the mechanisms of the pathogenesis of the disease has largely been limited by its inherent complexity imparted by the polygenicity and interactions with environmental factors. Since pathobiological events are initiated in the schizophrenic brain long before the onset of the psychotic manifestations, characterizing these processes is limited, mainly due to a lack of access to neuronal tissues. Induced pluripotent stem cell (iPSC) technologies have provided an unprecedented opportunity to establish pluripotent stem cells from patients with schizophrenia and differentiate them into neuronal lineage, enabling an in vitro recapitulation of the pathogenesis of the disease. Despite the inherent challenges, patient-derived iPSC studies of schizophrenia have been instrumental in unraveling the cellular and molecular phenotypes that might be involved in the biological causality. Here we review the literature and focus on studies that have utilized patient-derived iPSCs to model the pathogenesis of schizophrenia. We also discuss the challenges in modeling cellular phenotypes of schizophrenia.
Over the past years, systemic derived cues that regulate cellular metabolism have been implicated in the regulation of immune responses. Ghrelin is an orexigenic hormone produced by enteroendocrine cells in the gastric mucosa with known immunoregulatory roles. The mechanism behind the function of ghrelin in immune cells, such as macrophages, is still poorly understood. Here, we explored the hypothesis that ghrelin leads to alterations in macrophage metabolism thus modulating macrophage function. We demonstrated that ghrelin exerts an immunomodulatory effect over LPS-activated peritoneal macrophages, as evidenced by inhibition of TNF-α and IL-1β secretion and increased IL-12 production. Concomitantly, ghrelin increased mitochondrial membrane potential and increased respiratory rate. In agreement, ghrelin prevented LPS-induced ultrastructural damage in the mitochondria. Ghrelin also blunted LPS-induced glycolysis. In LPS-activated macrophages, glucose deprivation did not affect ghrelin-induced IL-12 secretion, whereas the inhibition of pyruvate transport and mitochondria-derived ATP abolished ghrelin-induced IL-12 secretion, indicating a dependence on mitochondrial function. Ghrelin pre-treatment of metabolic activated macrophages inhibited the secretion of TNF-α and enhanced IL-12 levels. Moreover, ghrelin effects on IL-12, and not on TNF-α, are dependent on mitochondria elongation, since ghrelin did not enhance IL-12 secretion in metabolic activated mitofusin-2 deficient macrophages. Thus, ghrelin affects macrophage mitochondrial metabolism and the subsequent macrophage function.
Neurobiological models of adolescent decision-making emphasize developmental changes in brain regions involved in affect (e.g., ventral striatum) and cognitive control (e.g., lateral prefrontal cortex). Although social context plays an important role in adolescent decision-making, current models do not discuss brain regions implicated in processing social information (e.g., dorsomedial prefrontal cortex). We conducted a coordinate-based meta-analysis using the Multilevel peak Kernel Density Analysis (MKDA) method to test the hypothesis that brain regions involved in affect, cognitive control, and social information processing support adolescent decision-making in social contexts (N = 21 functional neuroimaging studies; N = 1292 participants). Results indicated that dorsomedial prefrontal cortex, inferior frontal gyrus/insula and ventral striatum are consistently associated with adolescent decision-making in social contexts. Activity within these regions was modulated by the type of social context and social actors involved. Findings suggest including brain regions involved in social information processing into models of adolescent decision-making. We propose a ‘constructionist’ model, which describes psychological processes and corresponding neural networks related to affect, cognitive control, and social information processing.
We document the preparation and properties of dimerized pentaphosphate-bridged deoxynucleotides (dicaptides) that contain reactive components of two different nucleotides simultaneously. Importantly, dicaptides are found to be considerably more stable to hydrolysis than standard dNTPs. Steady-state kinetics studies show that the dimers exhibit reasonably good efficiency with the Klenow fragment of DNA polymerase I, and we identify thermostable enzymes that process them efficiently at high temperature. Experiments show that the dAp5dT dimer successfully acts as a combination of dATP and dTTP in primer extension reactions, and the dGp5dC dimer as a combination of dGTP and dCTP. The two dimers in combination promote successful 4-base primer extension. The final byproduct of the reaction, triphosphate, is shown to be less inhibitory to primer extension than pyrophosphate, the canonical byproduct. Finally, we document PCR amplification of DNA with two dimeric nucleotides, and show that the dimers can promote amplification under extended conditions when PCR with normal dNTPs fails. These dimeric nucleotides represent a novel and simple approach for increasing stability of nucleotides and avoiding inhibition from pyrophosphate.