Mechanism of hydrophobic gating in the acetylcholine receptor channel pore.

Neuromuscular acetylcholine receptors (AChRs) are hetero-pentameric, ligand-gated ion channels. The binding of the neurotransmitter acetylcholine (ACh) to two target sites promotes a global conformational change of the receptor that opens the channel and allows ion conduction through the channel pore. Here, by measuring free-energy changes from single-channel current recordings and using molecular dynamics simulations, we elucidate how a constricted hydrophobic region acts as a "gate" to regulate the channel opening in the pore of AChRs. Mutations of gate residues, including those implicated in congenital myasthenia syndrome, lower the permeation barrier of the channel substantially and increase the unliganded gating equilibrium constant (constitutive channel openings). Correlations between hydrophobicity and the observed free-energy changes, supported by calculations of water densities in the wild-type versus mutant channel pores, provide evidence for hydrophobic wetting-dewetting transition at the gate. The analysis of a coupled interaction network provides insight into the molecular mechanism of closed- versus open-state conformational changes at the gate. Studies of the transition state by "phi"(φ)-value analysis indicate that agonist binding serves to stabilize both the transition and the open state. Intersubunit interaction energy measurements and molecular dynamics simulations suggest that channel opening involves tilting of the pore-lining M2 helices, asymmetric outward rotation of amino acid side chains, and wetting transition of the gate region that lowers the barrier to ion permeation and stabilizes the channel open conformation. Our work provides new insight into the hydrophobic gate opening and shows why the gate mutations result in constitutive AChR channel activity.

Structure-function analysis suggests that the photoreceptor LITE-1 is a light-activated ion channel.

Sensation of light is essential for all organisms. The eye-less nematode Caenorhabditis elegans detects UV and blue light to evoke escape behavior. The photosensor LITE-1 absorbs UV photons with an unusually high extinction coefficient, involving essential tryptophans. Here, we modeled the structure and dynamics of LITE-1 using AlphaFold2-multimer and molecular dynamics (MD) simulations and performed mutational and behavioral assays in C. elegans to characterize its function. LITE-1 resembles olfactory and gustatory receptors from insects, recently shown to be tetrameric ion channels. We identified residues required for channel gating, light absorption, and mechanisms of photo-oxidation, involving a likely binding site for the peroxiredoxin PRDX-2. Furthermore, we identified the binding pocket for a putative chromophore. Several residues lining this pocket have previously been established as essential for LITE-1 function. A newly identified critical cysteine pointing into the pocket represents a likely chromophore attachment site. We derived a model for how photon absorption, via a network of tryptophans and other aromatic amino acids, induces an excited state that is transferred to the chromophore. This evokes conformational changes in the protein, possibly leading to a state receptive to oxidation of cysteines and, jointly, to channel gating. Electrophysiological data support the idea that LITE-1 is a photon and H2O2-coincidence detector. Other proteins with similarity to LITE-1, specifically C. elegans GUR-3, likely use a similar mechanism for photon detection. Thus, a common protein fold and assembly, used for chemoreception in insects, possibly by binding of a particular compound, may have evolved into a light-activated ion channel.

Evaluation of the Posttraumatic Stress Disorder Checklist for DSM-5 across United States and India samples: An item response theory analysis using the graded response model.

OBJECTIVES: The Posttraumatic Stress Disorder (PTSD) Checklist for DSM-5 (PCL-5) is frequently used to assess PTSD symptoms. Extending its psychometric investigations across distinct samples (United States and India), the aims of the present study included investigating the item characteristics, person fit, and differential item functioning (DIF) across the two samples. METHOD: We (a) conducted item analysis using the graded response model to examine item characteristics (thresholds and discrimination parameters) and (b) examined person fit to determine participants' response patterns. The U.S. sample included 176 trauma-exposed individuals seeking mental health treatment, and the Indian sample included 148 trauma-exposed ex-military personnel. RESULTS: Results indicated low discrimination for Item 8 and low but acceptable discrimination for Item 17 for the U.S. and Indian samples, respectively. Across both samples, the most unused response categories were the middle-point or extreme (higher severity) categories (all response categories were better utilized in the Indian sample), and half the participants exhibited person misfit. Supplemental DIF analysis indicated that five items exhibited DIF indicating potential item bias; however, effect sizes for DIF were negligible. CONCLUSIONS: Although the PCL-5 demonstrated strong psychometric properties and showed promise for use across the samples differing on cultural and demographic characteristics, some of the items and the number of categories used to measure them could be revisited to create a more efficient instrument. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Protein engineering and design in ion channels and receptors.

Acetylcholine receptors (AChRs) expressed at the neuromuscular junction synapses are typical allosteric proteins that shuttle between at least two stable conformational states: Closed (C) and Open (O). Agonist binding to their target sites on the receptor in the extracellular domain triggers a global C→O conformational change that results in an open channel pore that allows ion conduction. How the receptor senses the chemical signal of an agonist and communicates it to the channel pore, located ~50Šaway, are key to understanding the receptor function. AChRs are indispensable for muscle contraction and their neuronal homologues play critical roles in the nervous system function. In this chapter, using a combination of single channel patch-clamp, computational approaches, and genetic engineering, we elucidate the principles of design and engineering to quantify the fundamental thermodynamic parameters of AChRs that regulate ligand binding and channel opening. The receptor engineering principles outlined here for the neuromuscular AChRs are applicable to the broader class of ligand-gated ion channel proteins.

The relationship between number of trauma types, resilience, and psychological symptoms in ex-military personnel from India.

OBJECTIVE: Traumatic event (TE) types have been shown to relate to adverse psychological outcomes. However, research in this area has relied almost exclusively on linear analysis and has been limited to Western countries with similar cultural values. Addressing these limitations, this study examined (a) presence and nature of relations between number of TE types and psychological outcomes and (b) minimum number of TE types predicting psychological symptoms in a culturally distinct sample of ex-military members from India. METHOD: The sample of 144 trauma-exposed Indian ex-military members (Mage = 43.49; 90.90% males) completed a web-based survey. RESULTS: Curvilinear regression analyses indicated quadratic relationships between number of TE types and psychological symptoms (posttraumatic stress disorder [PTSD], depression, and anxiety severity) and resilience. Exploratory analyses showed (a) linear relationships between number of directly experienced TE types and psychological outcomes, (b) quadratic relationships between number of Predominant Death Threat TEs and psychological symptoms, (c) linear relationship between number of Predominant Death Threat TEs and resilience, and (d) linear relationships between other TE categories and psychological outcomes. Nonparametric receiver operating characteristic curve analyses indicated that a threshold of at least 10.5 TE types provided the optimal balance between sensitivity and specificity in classifying participants with (vs. without) probable PTSD, depression, and generalized anxiety disorder. For those reporting directly experienced TE types, this threshold was 2.5-3.5 TE types. CONCLUSION: Study results enhance an understanding of psychological difficulties faced by Indian ex-military members who have experienced multiple TE types, which can inform psychotherapeutic treatments for this population. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Comparison of latent typologies of posttraumatic stress disorder and depression symptoms across military personnel from India and the US.

Research has identified heterogeneous subgroups of individuals based on posttraumatic stress disorder (PTSD) and depression symptoms. Using data collected from military personnel in India (N = 146) and U.S. (N = 194), we examined (1) the best-fitting latent class solution; (2) multi-group invariance of the class solution; and (3) construct validity of optimal class solution. Results indicated that the optimal 4-class solution differed in severity and severity/type in the India and U.S. samples respectively. With similarity in the optimal number of classes across cultural samples, the meaning/nature of classes differed. In the India sample, anxiety severity predicted the Low Severity Class vs. all other classes, and the Moderately High Severity/High Severity Classes vs. the Moderately Low Severity Class; number of traumas predicted the High Severity Class vs. other classes; and resilience predicted the Moderately Low Severity Class vs. the Moderately High Severity Class. In the U.S. sample, alcohol use predicted the High Severity Class vs. all other classes, and the High Depression-Low PTSD Class vs. the Low Severity Class; rumination significantly predicted the High Severity and High Depression-Low PTSD Classes vs. each of the High PTSD-Low Depression and Low Severity Classes. Thus, meaning and nature of PTSD-depression subgroups may vary culturally; hence, culturally-sensitive interventions need to account for this heterogeneity.

Correction to: Behavioral Artistry: Examining the Relationship Between the Interpersonal Skills and Effective Practice Repertoires of Applied Behavior Analysis Practitioners.

The article Behavioral Artistry: Examining the Relationship Between the Interpersonal Skills and Effective Practice Repertoires of Applied Behavior Analysis Practitioners, written by Kevin Callahan, was originally published electronically on the publisher's internet portal (currently SpringerLink) on August 29, 2019 without open access. With the author(s)' decision to opt for Open Choice the copyright of the article changed on August, 2019 to © The Author(s) 2019 and the article is forthwith distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, duplication, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

Behavioral Artistry: Examining the Relationship Between the Interpersonal Skills and Effective Practice Repertoires of Applied Behavior Analysis Practitioners.

This study investigated interpersonal skills associated with the concept of behavioral artistry (BA), a repertoire of practitioner behaviors including care, attentiveness, and creativity, among others, associated with the effective delivery of applied behavior analysis (ABA) treatment. Survey results indicated parents of children with autism preferred BA descriptors for ABA therapists over non-BA descriptors. A separate survey of 212 university students on a standardized personality assessment revealed students majoring and/or working in the field of ABA had lower levels of BA than those in other human services professions. Practitioners with higher BA scores were observed and rated more positively in their delivery of ABA for children with autism. Implications for training/supervising effective ABA practitioners within a BA model are discussed.

Impairment of functioning and substance use in a Latino population.

This study investigated the association of academic outcomes, romantic relationships, and substance use (tobacco, marijuana, cocaine) with alcohol dependence in a sample of Latino (N = 1,143) college students. Secondary data analysis was conducted on measures of grade point average in college, relationship satisfaction, drug use, and alcohol dependence. Latino college students who reported alcohol dependency had significant relational dissatisfaction and poor academic outcomes. Thus, lower grade point average and relationship dissatisfaction were associated with alcohol dependence. By focusing specifically on a Mexican American population, this study adds important information to current research regarding the commonality and differences across cultural groups regarding drug use and dependence and further clarifies the risk factors associated with substance use and dependency in a population that is vulnerable for at-risk behaviors. This study also offers insight into potential targets of treatment and intervention for this cultural group.

Acculturation and substance use in a Mexican American college student sample.

Although the association between acculturation and substance use among Latino groups is important, it is often understudied, especially within specific Latino groups living in geographically distinct communities, such as the Mexican American population in South Texas. The researchers of this study aimed to better understand the effect of acculturation on substance use and alcohol dependence in a Mexican American college student population. This survey study investigated the correlation between acculturation and substance use and dependence by using the Vancouver Index of Acculturation (VIA), items related to substance use (nicotine, marijuana, and cocaine) in a Mexican American college student sample (N = 1,494), and the Short Alcohol Dependence Data Questionnaire (SADD; N = 715). The study was conducted in the Texas-Mexico border region. The results suggest that higher levels of acculturation do not predict increased drug use or alcohol dependence in the Mexican American college students. However, acculturation was found to be associated with lower use of cocaine and marijuana. The discussion examines commonalities and differences in drug use and dependence. Specifically, acculturation seems to have an inverse relationship to substance use and may serve as a protective factor to licit and illicit drug use among Mexican American college students.

On-chip microelectrode impedance analysis of mammalian cell viability during biomanufacturing.

The characterization of cell viability is a challenging task in applied biotechnology, as no clear definition of cell death exists. Cell death is accompanied with a change in the electrical properties of the membrane as well as the cell interior. Therefore, changes in the physiology of cells can be characterized by monitoring of their dielectric properties. We correlated the dielectric properties of industrially used mammalian cells, sedimented over interdigitated microelectrodes, to the AC signal response across the chip. The voltage waveforms across the electrodes were processed to obtain the circuit impedance, which was used to quantify the changes in cell viability. We observed an initial decrease in impedance, after which it remained nearly constant. The results were compared with data from the dye exclusion viability test, the cell specific oxygen uptake rate, and the online viable cell density data from capacitance probes. The microelectrode technique was found to be sensitive to physiological changes taking place inside the cells before their membrane integrity is compromised. Such accurate determination of the metabolic status during this initial period, which turned out to be less well captured in the dye exclusion tests, may be essential for several biotechnology operations.

Gel-based self-propelling particles get programmed to dance.

We present a class of gel-based self-propelling particles moving by the Marangoni effect in an oscillatory mode. The particles are made of an ethanol-infused polyacrylamide hydrogel contained in plastic tubing. These gel boats floating on the water surface exhibit periodic propulsion for several hours. The release of ethanol from the hydrogel takes place beneath the liquid surface. The released ethanol rises to the air-water interface by buoyancy and generates a self-sustained cycle of surface tension gradient driven motion. The disruption of the ethanol flux to the surface by the bulk flows around the moving particle results in their pulsating motion. The pulse interval and the distance propelled in a pulse by these gel floaters were measured and approximated by simple expressions based on the rate of ethanol mass-transfer through and out of the hydrogel. This allowed us to design a multitude of particles performing periodic steps in different directions or at different angles of rotation, traveling in complex preprogrammed trajectories on the surface of the liquid. Similar gel-based self-propelling floaters can find applications as mixers and cargo carriers in lab-on-a-chip devices, and in various platforms for sensing and processing at the microscale.

Regulatory link mapping between organisms.

BACKGROUND: Identification of gene regulatory networks is useful in understanding gene regulation in any organism. Some regulatory network information has already been determined experimentally for model organisms, but much less has been identified for non-model organisms, and the limited amount of gene expression data available for non-model organisms makes inference of regulatory networks difficult. RESULTS: This paper proposes a method to determine the regulatory links that can be mapped from a model to a non-model organism. Mapping a regulatory network involves mapping the transcription factors and target genes from one genome to another. In the proposed method, Basic Local Alignment Search Tool (BLAST) and InterProScan are used to map the transcription factors, whereas BLAST along with transcription factor binding site motifs and the GALF-P tool are used to map the target genes. Experiments are performed to map the regulatory network data of S. cerevisiae to A. thaliana and analyze the results. Since limited information is available about gene regulatory network links, gene expression data is used to analyze results. A set of rules are defined on the gene expression experiments to identify the predicted regulatory links that are well supported. CONCLUSIONS: Combining transcription factors mapped using BLAST and subfamily classification, together with target genes mapped using BLAST and binding site motifs, produced the best regulatory link predictions. More than two-thirds of these predicted regulatory links that were analyzed using gene expression data have been verified as correctly mapped regulatory links in the target genome.