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Background Impaired 5- HT3 receptor function is likely involved in the pathogenesis of functional gastrointestinal disorders ( FGID) and 5- HT3 receptor antagonists are effective treatments for chemotherapy-induced nausea and vomiting ( CINV) and irritable bowel syndrome ( IBS). The monoterpene alcohol menthol and the aporphine alkaloid boldine combat symptoms of gastrointestinal diseases; both interact with other members of the Cys-loop ligand-gated ion channel family and may therefore also act on 5- HT3 receptors. Methods The impact of boldine and menthol on human recombinant homomeric 5- HT3A- and heteromeric 5- HT3 AB receptors in HEK293 cells was determined by radioligand binding, a luminescence-based Ca2+ assay, and a membrane potential assay. 5- HT3 protein and m RNA expression was assessed in human colon tissue. Key Results Boldine and menthol inhibited the 5- HT-induced activation of 5- HT3 receptors in the low and middle micromolar range, respectively. Boldine was a competitive antagonist of both receptors being 6.5- to 10-fold more potent at 5- HT3A- vs 5- HT3 AB receptors. Menthol non-competitively and stereoselectively inhibited both receptors: In contrast to (+)-menthol, (−)-menthol was significantly more potent toward 5- HT3A- vs 5- HT3 AB receptors. We show co-expression of 5- HT3A and 5- HT3B subunits in the human gut epithelium, the lamina propria, the myenteric plexus, and the muscular cell layer. Conclusions & Inferences The demonstrated 5- HT3 inhibitory effects may be relevant for boldine's and menthol's alleviating properties on FGID and may encourage clinical studies with the compounds or the plant extracts for CINV and IBS treatment. The found receptor-discriminative properties make boldine and (−)-menthol to potentially useful tools for analyzing structural differences between these receptor subtypes. [ABSTRACT FROM AUTHOR]

Research was conducted to examine the 5-hydroxytryptamine receptor of type 3 A receptor (5HT(sub 3As)) using fluorescence correlation spectroscopy. The investigation focused on the different photophysical properties of the fluorophores which are representative for a wide range of labels and how their different molecular properties disturb the molecular interaction between the ligand and its receptor. Results show that with the combination of the fluorophores, the binding constants and the stoichiometry of ligand binding can be accurately measured and the relative molecular mass of the receptor can be calculated.

Functional membrane proteins in the plasma membrane are suggested to have specific membrane environments that play important roles to maintain and regulate their function. However, the local membrane environments of membrane proteins remain largely unexplored due to the lack of available techniques. We have developed a method to probe the local membrane environment surrounding membrane proteins in the plasma membrane by covalently tethering a solvatochromic, environment-sensitive dye, Nile Red, to a GPI-anchored protein and the insulin receptor through a flexible linker. The fluidity of the membrane environment of the GPI-anchored protein depended upon the saturation of the acyl chains of the lipid anchor. The local environment of the insulin receptor was distinct from the average plasma membrane fluidity and was quite dynamic and heterogeneous. Upon addition of insulin, the local membrane environment surrounding the receptor specifically increased in fluidity in an insulin receptor-kinase dependent manner and on the distance between the dye and the receptor., (© 2022 Umebayashi et al.)

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit., (Copyright © 2020 by The American Society for Pharmacology and Experimental Therapeutics.)

The inner nuclear membrane is functionalized by diverse transmembrane proteins that associate with nuclear lamins and/or chromatin. When cells enter mitosis, membrane-chromatin contacts must be broken to allow for proper chromosome segregation; yet how this occurs remains ill-understood. Unexpectedly, we observed that an imbalance in the levels of the lamina-associated polypeptide 1 (LAP1), an activator of ER-resident Torsin AAA+-ATPases, causes a failure in membrane removal from mitotic chromatin, accompanied by chromosome segregation errors and changes in post-mitotic nuclear morphology. These defects are dependent on a hitherto unknown chromatin-binding region of LAP1 that we have delineated. LAP1-induced NE abnormalities are efficiently suppressed by expression of wild-type but not ATPase-deficient Torsins. Furthermore, a dominant-negative Torsin induces chromosome segregation defects in a LAP1-dependent manner. These results indicate that association of LAP1 with chromatin in the nucleus can be modulated by Torsins in the perinuclear space, shedding new light on the LAP1-Torsin interplay., Competing Interests: NL, Jd, RH, DM, RL, RU, BF, UK No competing interests declared, (© 2020, Luithle et al.)

The DNA sensor cyclic GMP-AMP synthase (cGAS) initiates innate immune responses following microbial infection, cellular stress and cancer 1 . Upon activation by double-stranded DNA, cytosolic cGAS produces 2'3' cGMP-AMP, which triggers the induction of inflammatory cytokines and type I interferons  2-7 . cGAS is also present inside the cell nucleus, which is replete with genomic DNA 8 , where chromatin has been implicated in restricting its enzymatic activity 9 . However, the structural basis for inhibition of cGAS by chromatin remains unknown. Here we present the cryo-electron microscopy structure of human cGAS bound to nucleosomes. cGAS makes extensive contacts with both the acidic patch of the histone H2A-H2B heterodimer and nucleosomal DNA. The structural and complementary biochemical analysis also find cGAS engaged to a second nucleosome in trans. Mechanistically, binding of the nucleosome locks cGAS into a monomeric state, in which steric hindrance suppresses spurious activation by genomic DNA. We find that mutations to the cGAS-acidic patch interface are sufficient to abolish the inhibitory effect of nucleosomes in vitro and to unleash the activity of cGAS on genomic DNA in living cells. Our work uncovers the structural basis of the interaction between cGAS and chromatin and details a mechanism that permits self-non-self discrimination of genomic DNA by cGAS.

Pioneer transcription factors (pTFs) bind to target sites within compact chromatin, initiating chromatin remodeling and controlling the recruitment of downstream factors. The mechanisms by which pTFs overcome the chromatin barrier are not well understood. Here, we reveal, using single-molecule fluorescence, how the yeast transcription factor Rap1 invades and remodels chromatin. Using a reconstituted chromatin system replicating yeast promoter architecture, we demonstrate that Rap1 can bind nucleosomal DNA within a chromatin fiber but with shortened dwell times compared to naked DNA. Moreover, we show that Rap1 binding opens chromatin fiber structure by inhibiting inter-nucleosome contacts. Finally, we reveal that Rap1 collaborates with the chromatin remodeler RSC to displace promoter nucleosomes, paving the way for long-lived bound states on newly exposed DNA. Together, our results provide a mechanistic view of how Rap1 gains access and opens chromatin, thereby establishing an active promoter architecture and controlling gene expression., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.)

Optical monitoring of neuronal voltage using fluorescent indicators is a powerful approach for the interrogation of the cellular and molecular logic of the nervous system. Herein, a semisynthetic tethered voltage indicator (STeVI1) based upon nile red is described that displays voltage sensitivity when genetically targeted to neuronal membranes. This environmentally sensitive probe allows for wash-free imaging and faithfully detects supra- and sub-threshold activity in neurons., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)