Nanoscale Mobility of the Apo State and TARP Stoichiometry Dictate the Gating Behavior of Alternatively Spliced AMPA Receptors.

Neurotransmitter-gated ion channels are allosteric proteins that switch on and off in response to agonist binding. Most studies have focused on the agonist-bound, activated channel while assigning a lesser role to the apo or resting state. Here, we show that nanoscale mobility of resting α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type ionotropic glutamate receptors (AMPA receptors) predetermines responsiveness to neurotransmitter, allosteric anions and TARP auxiliary subunits. Mobility at rest is regulated by alternative splicing of the flip/flop cassette of the ligand-binding domain, which controls motions in the distant AMPA receptor N-terminal domain (NTD). Flip variants promote moderate NTD movement, which establishes slower channel desensitization and robust regulation by anions and auxiliary subunits. In contrast, greater NTD mobility imparted by the flop cassette acts as a master switch to override allosteric regulation. In AMPA receptor heteromers, TARP stoichiometry further modifies these actions of the flip/flop cassette generating two functionally distinct classes of partially and fully TARPed receptors typical of cerebellar stellate and Purkinje cells

Distinct Structural Pathways Coordinate the Activation of AMPA Receptor-Auxiliary Subunit Complexes

SummaryNeurotransmitter-gated ion channels adopt different gating modes to fine-tune signaling at central synapses. At glutamatergic synapses, high and low activity of AMPA receptors (AMPARs) is observed when pore-forming subunits coassemble with or without auxiliary subunits, respectively. Whether a common structural pathway accounts for these different gating modes is unclear. Here, we identify two structural motifs that determine the time course of AMPAR channel activation. A network of electrostatic interactions at the apex of the AMPAR ligand-binding domain (LBD) is essential for gating by pore-forming subunits, whereas a conserved motif on the lower, D2 lobe of the LBD prolongs channel activity when auxiliary subunits are present. Accordingly, channel activity is almost entirely abolished by elimination of the electrostatic network but restored via auxiliary protein interactions at the D2 lobe. In summary, we propose that activation of native AMPAR complexes is coordinated by distinct structural pathways, favored by the association/dissociation of auxiliary subunits

Defining the structural relationship between kainate-receptor deactivation and desensitization

nature structural & molecular biology advance online publication a r t i c l e s Structural and functional biologists have long sought to understand the mechanisms by which LGICs respond to small chemical ligands and modulators. Seminal work established the general principle that LGICs not only are activated by biologically derived molecules, such as the neurotransmitter acetylcholine 1 , but also are inactivated by prolonged exposure to these molecules through a process universally known as desensitization 2 . Since this work, almost all LGICs have been shown to desensitize. For example, desensitization is thought to shape signaling within the vertebrate central nervous system by affecting the fast chemical transmission mediated by iGluRs along with GABA A and glycine receptors 3 . From all of this work, it has been concluded that the conformational events that lead to the occurrence of deactivation and the onset of desensitization are governed by the physicochemical properties of the bound ligand 4 . In support of this, pioneering work on native AMPA-type iGluRs (AMPARs) has shown that even modest changes to the ligand structure have profound effects on the rates and degree of desensitization 5 . During the last decade, structural and functional analyses of LGICs have revealed that the molecular basis of channel gating may be quite distinct for different ion-channel families Here, we set out to study the molecular basis of KAR desensitization by evaluating mutants that are proposed to block it RESULTS KARs desensitize with or without prior channel activation To observe the microscopic behavior of KAR desensitization, we excised outside-out patches from transfected mammalian cells Desensitization is an important mechanism curtailing the activity of ligand-gated ion channels (LGICs). Although the structural basis of desensitization is not fully resolved, it is thought to be governed by physicochemical properties of bound ligands. Here, we show the importance of an allosteric cation-binding pocket in controlling transitions between activated and desensitized states of rat kainate-type (KAR) ionotropic glutamate receptors (iGluRs). Tethering a positive charge to this pocket sustains KAR activation, preventing desensitization, whereas mutations that disrupt cation binding eliminate channel gating. These different outcomes explain the structural distinction between deactivation and desensitization. Deactivation occurs when the ligand unbinds before the cation, whereas desensitization proceeds if a ligand is bound without cation pocket occupancy. This sequence of events is absent from AMPA-type iGluRs; thus, cations are identified as gatekeepers of KAR gating, a role unique among even closely related LGICs

Mineral carbonation of serpentinite: From the Laboratory to Pilot Scale - The MCi project

To date, ex-situ carbonation of ultramafic ores such as serpentinite has been studied extensively on the laboratory scale. In Australia, the Mineral Carbonation International (MCi) project was launched in 2013, with funding from the New South Wales (NSW) State and the Australian Federal Governments as well as an industry partner, Orica. The project aims to demonstrate the techno-economic viability of mineral carbonation as a sustainable industrial solution for carbon capture, storage and utilisation (CCSU). For the first time, mineral carbonation of silicate ore will be studied at a scale several orders of magnitude greater than laboratory scales hitherto. The MCi project is believed to be the first holistic approach to CCSU via mineral carbonation, examining the full chain of operations from feedstock to final product. It comprises three core themes; the construction and operation of a research pilot plant, a portfolio of research projects and support activities and commercialisation. The research encompasses mineral mapping, characterisation, processing and pretreatment through to process integration with power generation and CO 2 capture, fundamentals of carbonation chemistry, value-adding and final product storage. In line with this holistic approach, Life Cycle Assessments (LCAs) are being conducted

Secondary attack rates in primary and secondary school bubbles following a confirmed case: Active, prospective national surveillance, November to December 2020, England.

BACKGROUND: Following the full re-opening of schools in England and emergence of the SARS-CoV-2 Alpha variant, we investigated the risk of SARS-CoV-2 infection in students and staff who were contacts of a confirmed case in a school bubble (school groupings with limited interactions), along with their household members. METHODS: Primary and secondary school bubbles were recruited into sKIDsBUBBLE after being sent home to self-isolate following a confirmed case of COVID-19 in the bubble. Bubble participants and their household members were sent home-testing kits comprising nasal swabs for RT-PCR testing and whole genome sequencing, and oral fluid swabs for SARS-CoV-2 antibodies. RESULTS: During November-December 2020, 14 bubbles were recruited from 7 schools, including 269 bubble contacts (248 students, 21 staff) and 823 household contacts (524 adults, 299 children). The secondary attack rate was 10.0% (6/60) in primary and 3.9% (4/102) in secondary school students, compared to 6.3% (1/16) and 0% (0/1) among staff, respectively. The incidence rate for household contacts of primary school students was 6.6% (12/183) and 3.7% (1/27) for household contacts of primary school staff. In secondary schools, this was 3.5% (11/317) and 0% (0/1), respectively. Household contacts were more likely to test positive if their bubble contact tested positive although there were new infections among household contacts of uninfected bubble contacts. INTERPRETATION: Compared to other institutional settings, the overall risk of secondary infection in school bubbles and their household contacts was low. Our findings are important for developing evidence-based infection prevention guidelines for educational settings

Epidemiology of SARS-CoV-2 infection among staff and students in a cohort of English primary and secondary schools during 2020–2021

BACKGROUND: There remains uncertainty about the epidemiology of SARS-CoV-2 among school students and staff and the extent to which non-pharmaceutical-interventions reduce the risk of school settings. METHODS: We conducted an open cohort study in a sample of 59 primary and 97 secondary schools in 15 English local authority areas that were implementing government guidance to schools open during the pandemic. We estimated SARS-CoV-2 infection prevalence among those attending school, antibody prevalence, and antibody negative to positive conversion rates in staff and students over the school year (November 2020–July 2021). FINDINGS: 22,585 staff and students participated. SARS-CoV-2 infection prevalence among those attending school was highest during the first two rounds of testing in the autumn term, ranging from 0.7% (95% CI 0.2, 1.2) among primary staff in November 2020 to 1.6% (95% CI 0.9, 2.3) among secondary staff in December 2020. Antibody conversion rates were highest in the autumn term. Infection patterns were similar between staff and students, and between primary and secondary schools. The prevalence of nucleoprotein antibodies increased over the year and was lower among students than staff. SARS-CoV-2 infection prevalence in the North-West region was lower among secondary students attending school on normal school days than the regional estimate for secondary school-age children. INTERPRETATION: SARS-CoV-2 infection prevalence in staff and students attending school varied with local community infection rates. Non-pharmaceutical interventions intended to prevent infected individuals attending school may have partially reduced the prevalence of infection among those on the school site. FUNDING: UK Department of Health and Social Care