Fabrice Marger

Dithiol amino acids can structurally shape and enhance the ligand-binding properties of polypeptides

The disulfide bonds that form between two cysteine residues are important in defining and rigidifying the structures of proteins and peptides. In polypeptides containing multiple cysteine residues, disulfide isomerization can lead to multiple products with different biological activities. Here, we describe the development of a dithiol amino acid (Dtaa) that can form two disulfide bridges at a single amino acid site. Application of Dtaas to a serine protease inhibitor and a nicotinic acetylcholine receptor inhibitor that contain disulfide constraints enhanced their inhibitory activities 40- and 7.6-fold, respectively. X-ray crystallographic and NMR structure analysis show that the peptide ligands containing Dtaas have retained their native tertiary structures. We furthermore show that replacement of two cysteines by Dtaas can avoid the formation of disulfide bond isomers. With these properties, Dtaas are likely to have broad application in the rational design or directed evolution of peptides and proteins with high activity and stability.

T-type calcium channels contribute to colonic hypersensitivity in a rat model of irritable bowel syndrome.

The symptoms of irritable bowel syndrome (IBS) include significant abdominal pain and bloating. Current treatments are empirical and often poorly efficacious, and there is a need for the development of new and efficient analgesics aimed at IBS patients. T-type calcium channels have previously been validated as a potential target to treat certain neuropathic pain pathologies. Here we report that T-type calcium channels encoded by the CaV3.2 isoform are expressed in colonic nociceptive primary afferent neurons and that they contribute to the exaggerated pain perception in a butyrate-mediated rodent model of IBS. Both the selective genetic inhibition of CaV3.2 channels and pharmacological blockade with calcium channel antagonists attenuates IBS-like painful symptoms. Mechanistically, butyrate acts to promote the increased insertion of CaV3.2 channels into primary sensory neuron membranes, likely via a posttranslational effect. The butyrate-mediated regulation can be recapitulated with recombinant CaV3.2 channels expressed in HEK cells and may provide a convenient in vitro screening system for the identification of T-type channel blockers relevant to visceral pain. These results implicate T-type calcium channels in the pathophysiology of chronic visceral pain and suggest CaV3.2 as a promising target for the development of efficient analgesics for the visceral discomfort and pain associated with IBS.

Temperature-dependent Modulation of CaV3 T-type Calcium Channels by Protein Kinases C and A in Mammalian Cells

Modulation of low voltage-activated CaV3 T-type calcium channels remains poorly characterized compared with high voltage-activated CaV1 and CaV2 calcium channels. Notably, it is yet unresolved whether CaV3 channels are modulated by protein kinases in mammalian cells. In this study, we demonstrate that protein kinase A (PKA) and PKC (but not PKG) activation induces a potent increase in CaV3.1, CaV3.2, and CaV3.3 currents in various mammalian cell lines. Notably, we show that protein kinase effects occur at physiological temperature (∼30–37 °C) but not at room temperature (∼22–27 °C). This temperature dependence could involve kinase translocation, which is impaired at room temperature. A similar temperature dependence was observed for PKC-mediated increase in high voltage-activated CaV2.3 currents. We also report that neither CaV3 surface expression nor T-current macroscopic properties are modified upon kinase activation. In addition, we provide evidence for the direct phosphorylation of CaV3.2 channels by PKA in in vitro assays. Overall, our results clearly establish the role of PKA and PKC in the modulation of CaV3 T-channels and further highlight the key role of the physiological temperature in the effects described.

Therapeutic Potential of α7 Nicotinic Acetylcholine Receptors

Progress in the fields of neuroscience and molecular biology has identified the forebrain cholinergic system as being important in many higher order brain functions. Further analysis of the genes encoding the nicotinic acetylcholine receptors (nAChRs) has highlighted, in particular, the role of α7 nAChRs in these higher order brain functions as evidenced by their peculiar physiologic and pharmacological properties. As this receptor has gained the attention of scientists from academia and industry, our knowledge of its roles in various brain and bodily functions has increased immensely. We have also seen the development of small molecules that have further refined our understanding of the roles of α7 nAChRs, and these molecules have begun to be tested in clinical trials for several indications. Although a large body of data has confirmed a role of α7 nAChRs in cognition, the translation of small molecules affecting α7 nAChRs into therapeutics has to date only progressed to the stage of testing in clinical trials. Notably, however, most recent human genetic and biochemical studies are further underscoring the crucial role of α7 nAChRs and associated genes in multiple organ systems and disease states. The aim of this review is to discuss our current knowledge of α7 nAChRs and their relevance as a target in specific functional systems and disease states.

An internally modulated, thermostable, pH sensitive Cys-loop receptor from the hydrothermal vent worm Alvinella pompejana

Background: Cys loop receptors from the hydrothermal vent worm Alvinella pompejana were studied. Results: A Cys loop receptor opens at low pH, is chloride-specific, is modulated by its N-terminal extension, and is modestly thermostable. Conclusion: Cys loop receptors from worms living in extreme and secluded habitats are more closely related to eukaryotic than to prokaryotic family members. Significance: We studied the first known Cys loop receptor from a hydrothermal vent worm. Cys loop receptors (CLRs) are commonly known as ligand-gated channels that transiently open upon binding of neurotransmitters to modify the membrane potential. However, a class of cation-selective bacterial homologues of CLRs have been found to open upon a sudden pH drop, suggesting further ligands and more functions of the homologues in prokaryotes. Here we report an anion-selective CLR from the hydrothermal vent annelid worm Alvinella pompejana that opens at low pH. A. pompejana expressed sequence tag databases were explored by us, and two full-length CLR sequences were identified, synthesized, cloned, expressed in Xenopus oocytes, and studied by two-electrode voltage clamp. One channel, named Alv-a1-pHCl, yielded functional receptors and opened upon a sudden pH drop but not by other known agonists. Sequence comparison showed that both CLR proteins share conserved characteristics with eukaryotic CLRs, such as an N-terminal helix, a cysteine loop motif, and an intracellular loop intermediate in length between the long loops of other eukaryotic CLRs and those of prokaryotic CLRs. Both full-length Alv-a1-pHCl and a truncated form, termed tAlv-a1-pHCl, lacking 37 amino-terminal residues that precede the N-terminal helix, formed functional channels in oocytes. After pH activation, tAlv-a1-pHCl showed desensitization and was not modulated by ivermectin. In contrast, pH-activated, full-length Alv-a1-pHCl showed a marked rebound current and was modulated significantly by ivermectin. A thermostability assay indicated that purified tAlv-a1-pHCl expressed in Sf9 cells denatured at a higher temperature than the nicotinic acetylcholine receptor from Torpedo californica.