Regulation of HuR structure and function by dihydrotanshinone-I.

The Human antigen R protein (HuR) is an RNA-binding protein that recognizes U/AU-rich elements in diverse RNAs through two RNA-recognition motifs, RRM1 and RRM2, and post-transcriptionally regulates the fate of target RNAs. The natural product dihydrotanshinone-I (DHTS) prevents the association of HuR and target RNAs in vitro and in cultured cells by interfering with the binding of HuR to RNA. Here, we report the structural determinants of the interaction between DHTS and HuR and the impact of DHTS on HuR binding to target mRNAs transcriptome-wide. NMR titration and Molecular Dynamics simulation identified the residues within RRM1 and RRM2 responsible for the interaction between DHTS and HuR. RNA Electromobility Shifts and Alpha Screen Assays showed that DHTS interacts with HuR through the same binding regions as target RNAs, stabilizing HuR in a locked conformation that hampers RNA binding competitively. HuR ribonucleoprotein immunoprecipitation followed by microarray (RIP-chip) analysis showed that DHTS treatment of HeLa cells paradoxically enriched HuR binding to mRNAs with longer 3'UTR and with higher density of U/AU-rich elements, suggesting that DHTS inhibits the association of HuR to weaker target mRNAs. In vivo, DHTS potently inhibited xenograft tumor growth in a HuR-dependent model without systemic toxicity.

Electrostatic and Structural Bases of Fe2+ Translocation through Ferritin Channels.

Ferritin molecular cages are marvelous 24-mer supramolecular architectures that enable massive iron storage (>2000 iron atoms) within their inner cavity. This cavity is connected to the outer environment by two channels at C3 and C4 symmetry axes of the assembly. Ferritins can also be exploited as carriers for in vivo imaging and therapeutic applications, owing to their capability to effectively protect synthetic non-endogenous agents within the cage cavity and deliver them to targeted tissue cells without stimulating adverse immune responses. Recently, X-ray crystal structures of Fe2+-loaded ferritins provided important information on the pathways followed by iron ions toward the ferritin cavity and the catalytic centers within the protein. However, the specific mechanisms enabling Fe2+ uptake through wild-type and mutant ferritin channels is largely unknown. To shed light on this question, we report extensive molecular dynamics simulations, site-directed mutagenesis, and kinetic measurements that characterize the transport properties and translocation mechanism of Fe2+ through the two ferritin channels, using the wild-type bullfrog Rana catesbeiana H' protein and some of its variants as case studies. We describe the structural features that determine Fe2+ translocation with atomistic detail, and we propose a putative mechanism for Fe2+ transport through the channel at the C3 symmetry axis, which is the only iron-permeable channel in vertebrate ferritins. Our findings have important implications for understanding how ion permeation occurs, and further how it may be controlled via purposely engineered channels for novel biomedical applications based on ferritin.

Introducing an artificial photo-switch into a biological pore: A model study of an engineered α-hemolysin.

In recent years, engineered biological pores responsive to external stimuli have been fruitfully used for various biotechnological applications. Moreover, the strategy of tethering photo-switchable moieties into biomolecules has provided an unprecedented temporal control of purposely designed nanodevices, as demonstrated, for example, by the light-mediated regulation of the activity of enzymes and biochannels. Inspired by these advancements, we propose here a de novo designed nanodevice featuring the α-hemolysin (αHL) membrane channel purposely functionalized by an artificial "on/off" molecular switch. The switch, which is based on the photo-isomerization of the azobenzene moiety, introduces a smart nano-valve into the natural non-gated pore to confer tunable transport properties. We validated through molecular dynamics simulations and free energy calculations the effective inter-conversion of the engineered αHL pore between two configurations corresponding to an "open" and a "closed" form. The reported switchable translocation of a single-stranded DNA fragment under applied voltage supports the promising capabilities of this nanopore prototype in view of molecular sensing, detection and delivery applications at single-molecule level.

Understanding the role of dynamics in the iron sulfur cluster molecular machine.

BACKGROUND: The bacterial proteins IscS, IscU and CyaY, the bacterial orthologue of frataxin, play an essential role in the biological machine that assembles the prosthetic FeS cluster groups on proteins. They form functionally binary and ternary complexes both in vivo and in vitro. Yet, the mechanism by which they work remains unclear. METHODS: We carried out extensive molecular dynamics simulations to understand the nature of their interactions and the role of dynamics starting from the crystal structure of a IscS-IscU complex and the experimentally-based model of a ternary IscS-IscU-CyaY complex and used nuclear magnetic resonance to experimentally test the interface. RESULTS: We show that, while being firmly anchored to IscS, IscU has a pivotal motion around the interface. Our results also describe how the catalytic loop of IscS can flip conformation to allow FeS cluster assembly. This motion is hampered in the ternary complex explaining its inhibitory properties in cluster formation. CONCLUSIONS: We conclude that the observed 'fluid' IscS-IscU interface provides the binary complex with a functional adaptability exploited in partner recognition and unravels the molecular determinants of the reported inhibitory action of CyaY in the IscS-IscU-CyaY complex explained in terms of the hampering effect on specific IscU-IscS movements. GENERAL SIGNIFICANCE: Our study provides the first mechanistic basis to explain how the IscS-IscU complex selects its binding partners and supports the inhibitory role of CyaY in the ternary complex.

Cost-effectiveness analysis of mosunetuzumab for treatment of relapsed or refractory follicular lymphoma after two or more lines of systemic therapy in the United States.

AIMS: Mosunetuzumab has received accelerated approval by the US Food and Drug Administration for adult patients with relapsed or refractory (R/R) follicular lymphoma (FL) after two or more lines of systemic therapy. We evaluated the cost-effectiveness of mosunetuzumab for the treatment of R/R FL from a US private payer perspective. MATERIALS AND METHODS: A partitioned survival model simulated lifetime costs and outcomes of mosunetuzumab against seven comparators: axicabtagene ciloleucel (axi-cel), tisagenlecleucel (tisa-cel), tazemetostat (taz, EZH2 wild-type only), rituximab plus lenalidomide (R-Len) or bendamustine (R-Benda), obinutuzumab plus bendamustine (O-Benda), and a retrospective real-world cohort (RW) based on current patterns of care derived from US electronic health records (Flatiron Health). Efficacy data for mosunetuzumab were from the pivotal Phase II GO29781 trial (NCT02500407). Relative treatment efficacy was estimated from indirect treatment comparisons (ITCs). Costs included were related to treatment, adverse events, routine care, and terminal care. Except for drug costs (March 2023), all costs were inflated to 2022 US dollars. Costs and quality-adjusted life-years (QALYs) were used to calculate incremental cost-effectiveness ratios (ICERs). Net monetary benefit (NMB) was calculated using a willingness-to-pay (WTP) threshold of $150,000/QALY. RESULTS: Mosunetuzumab dominated taz, tisa-cel, and axi-cel with greater QALYs and lower costs. Mosunetuzumab was projected to be cost-effective against R-Benda, O-Benda, and RW with ICERs of $78,607, $42,731, and $21,434, respectively. Mosunetuzumab incurred lower costs but lower QALYs vs. R-Len. NMBs showed that mosunetuzumab was cost-effective against comparators except R-Len. LIMITATIONS: Without head-to-head comparative data, the model had to rely on ITCs, some of which were affected by residual bias. Model inputs were obtained from multiple sources. Extensive sensitivity analyses assessed the importance of these uncertainties. CONCLUSION: Mosunetuzumab is estimated to be cost-effective compared with approved regimens except R-Len for the treatment of adults with R/R FL.

Cost and Quality of Life of Disability Progression in Multiple Sclerosis Beyond EDSS: Impact of Cognition, Fatigue, and Limb Impairment.

BACKGROUND AND OBJECTIVE: Understanding the socioeconomic burden of multiple sclerosis (MS) is essential to inform policymakers and payers. Real-world studies have associated increasing costs and worsening quality of life (QoL) with disability progression. This study aims to further evaluate the impact of cognition, fatigue, upper and lower limb function (ULF, LLF) impairments, and disease progression per Expanded Disability Status Scale (EDSS) level, on costs and QoL. METHODS: This was a cross-sectional cohort study including 20,988 patients from the German NeuroTransData MS registry from 2009 to 2019. QoL analyses were based on EQ-5D-5L. Cost analyses included indirect/direct medical and non-medical costs. Eight subgroups, ranging from 439 to 1812 patients were created based on presence of measures for disease progression (EDSS), cognition (Symbol Digit Modalities Test [SDMT]), fatigue (Modified Fatigue Impact 5-Item Scale [MFIS-5]), ULF (Nine-Hole Peg Test [9HPT]), and LLF (Timed 25-Foot Walk [T25FW]). Multivariable linear regression assessed the independent effect of each test's score on QoL and costs, while adjusting for EDSS and 12 other confounders. RESULTS: Lower QoL was associated with decreasing cognition (p < 0.001), worsening ULF (p = 0.025), and increasing fatigue (p < 0.0001); however, the negative impact of LLF worsening on QoL was not statistically significant (p = 0.54). Higher costs were associated with decreasing cognition (p < 0.001), worsening of ULF (p = 0.0058) and LLF (p = 0.049), and increasing fatigue (p < 0.0001). Each 1-scale-step worsening function of SDMT, MFIS-5, 9HPT, and T25FW scores resulted in €170, €790, €330, and €520 higher costs, respectively. Modeling disability progression based on SDMT, MFIS-5, 9HPT, and T25FW scores as an interaction with EDSS strata found associations with lower QoL and higher costs at variable EDSS ranges. CONCLUSIONS: Disease progression in MS measured by 9HPT, SDMT, and MFIS-5 had a significant negative impact on QoL and broad socioeconomic costs independent of EDSS. T25FW had a significant negative association with costs. Cognition, fatigue, ULF, and LLF have stronger impact on costs and QoL in patients with higher EDSS scores. Additional determinants of MS disability status, including SDMT, MFIS-5, 9HPT, and T25FW, should be considered for assessing cost effectiveness of novel therapeutics for MS.

Systematic Literature Review to Identify Cost and Resource Use Data in Patients with Early-Stage Non-small Cell Lung Cancer (NSCLC).

BACKGROUND: Approximately 2 million new cases and 1.76 million deaths occur annually due to lung cancer, with the main histological subtype being non-small cell lung cancer (NSCLC). The costs and resource use associated with NSCLC are important considerations to understand the economic impact imposed by the disease on patients, caregivers and healthcare services. OBJECTIVE: The objective of this systematic literature review (SLR) is to provide a comprehensive overview of the available direct medical costs, direct non-medical costs, indirect costs, cost drivers and resource use data available for patients with early-stage NSCLC. METHODS: Electronic searches were conducted via the Ovid platform in March 2021 and June 2022 and were supplemented by grey literature searches. Eligible patients had early-stage (stage I-III) resectable NSCLC and received treatment in the neoadjuvant or adjuvant setting. There was no restriction on intervention or comparators. Publication date was restricted to 2011 onwards, and English language publications or non-English language publications with an English abstract were of primary interest. Due to the anticipation of many studies meeting the inclusion criteria, analyses were restricted to full publications from countries of primary interest (Australia, Brazil, Canada, China, France, Germany, Italy, Japan, South Korea, Spain, UK and the US) and those with > 200 patients. The Molinier checklist was applied to conduct quality assessment. RESULTS: Forty-two full publications met the eligibility criteria and were included in this SLR. Early-stage NSCLC was associated with significant direct medical costs and healthcare utilisation, and the economic burden of the disease increased with its progression. Surgery was the primary cost driver in stage I patients, but as patients progressed to stage II and III, treatments such as chemotherapy and radiotherapy, and inpatient care became the main cost drivers. There was no significant difference in resource use between patients with early-stage disease. However, these data were heavily US-centric and there was a paucity of data relating to direct non-medical and indirect costs associated with early-stage NSCLC. CONCLUSIONS: Preventing disease progression for patients with NSCLC could reduce the economic burden of NSCLC on patients, caregivers and healthcare systems. This review provides a comprehensive overview of the available cost and resource use data in this indication, which is important in guiding the decisions of policy makers regarding the allocation of resources. However, it also indicates a need for more studies comparing the economic impact of NSCLC in markets in addition to the US.

Health State Utility Values in Early-Stage Non-small Cell Lung Cancer: A Systematic Literature Review.

BACKGROUND: Non-small cell lung cancer (NSCLC) is the predominant histological subtype of lung cancer and is the leading cause of cancer-related deaths globally. Quality of life is an important consideration for patients and current treatments can adversely affect health-related quality of life (HRQoL). OBJECTIVE: The objectives of this systematic literature review (SLR) were to identify and provide a comprehensive catalogue of published health state utility values (HSUVs) in patients with early-stage NSCLC and to understand the factors impacting on HSUVs in this indication. METHODS: Electronic searches of Embase, MEDLINE and Evidence-Based Medicine Reviews were conducted via the Ovid platform in March 2021 and June 2022 and were supplemented by grey literature searches of conference proceedings, reference lists, health technology assessment bodies, and other relevant sources. Eligibility criteria were based on patients with early-stage (stage I-III) resectable NSCLC receiving treatment in the adjuvant or neoadjuvant setting. No restriction was placed on interventions or comparators, geography, or publication date. English language publications or non-English language publications with an English abstract were of primary interest. A validated checklist was applied to conduct quality assessment of the full publications. RESULTS: Twenty-nine publications (27 full publications and two conference abstracts) met all eligibility criteria and reported 217 HSUVs and seven disutilities associated with patients with early NSCLC. The data showed that increasing disease stage is associated with decreasing HRQoL. It was also indicated that utility values vary by treatment approach; however, the choice of treatment may be influenced by the patients' disease stage at presentation. Few studies aligned with the requirements of health technology assessment (HTA) bodies, indicating a need for future studies to conform to these preferences, making them suitable for use in economic evaluations. CONCLUSIONS: This SLR found that disease stage and treatment approach were two of several factors that can impact patient-reported HRQoL. Additional studies are warranted to confirm these findings and to investigate emerging therapies for early NSCLC. In collecting a catalogue of HSUV data, this SLR has begun to identify the challenges associated with identifying reliable utility value estimates suitable for use in economic evaluations of early NSCLC.

Cost-effectiveness analysis of adjuvant atezolizumab in stage II-IIIA non-small cell lung cancer expressing ≥50% PD-L1: A United Kingdom health care perspective.

OBJECTIVES: Atezolizumab monotherapy has marketing authorisation by the Medicines and Healthcare products Regulatory Agency as adjuvant treatment following complete resection for adults with stage II-IIIA non-small cell lung cancer (NSCLC) whose tumours have PD-L1 expression on ≥ 50% of tumour cells and whose disease has not progressed following adjuvant platinum-based chemotherapy. This study evaluated the cost-effectiveness of atezolizumab vs best supportive care (BSC) in the licensed patient population from a UK perspective. MATERIALS AND METHODS: Patient characteristics and clinical inputs were derived from the global, randomised, open-label, phaseIII IMpower010 trial. A Markov model with the following health states was developed: disease-free survival (DFS), locoregional recurrence, first-line metastatic recurrence, second-line metastatic recurrence, and death (all partitioned based on receipt of treatment, excluding death). The base case model used a lifetime time horizon (40 years) and 3.5% discounting annually after the first year. DFS from IMpower010 was analysed with parametric survival models to extrapolate outcomes for time points beyond trial follow-up. The models were adjusted to avoid overestimating results for patients with recurrences in the longer term. Grade ≥ 3 treatment-related adverse events with incidences ≥ 2% were included. Health state utility values were derived from the literature and past NICE appraisals. Sensitivity and scenario analyses assessed uncertainty around assumptions and parameter estimates. RESULTS: In the base case analysis, atezolizumab therapy resulted in an expected gain of 1.87 quality-adjusted life-years (QALYs) corresponding to an incremental cost-effectiveness ratio of £20,392/QALY for atezolizumab vs BSC, demonstrating cost-effectiveness. Results were most influenced by discount effects and utility in the on-treatment DFS state. Scenario analyses were consistent with the base case results. CONCLUSION: Atezolizumab after adjuvant chemotherapy is cost-effective for adults with NSCLC in the UK.

Survival and quality-of-life outcomes in early-stage NSCLC patients: a literature review of real-world evidence.

Aim: Assess the long-term survival and quality-of-life outcomes in early-stage NSCLC (eNSCLC) patients. Methods: Review of long-term survival and quality-of-life after curative treatment in eNSCLC patients in observational studies. Results: Disease-free proportion decreased in stage III vs stage I patients. Recurrence-free proportion decreased with age and disease stage. Advanced stage and vascular invasion increased risk of late recurrence. Conditional 5-year relative survival rates did not exceed 87%, indicating higher mortality in eNSCLC survivors. Lower conditional survival rates and relative survival rates were associated with older age and advanced disease. Survivors of eNSCLC had poorer physical quality-of-life. Conclusion: Despite curative-intent therapy, survivors of eNSCLC still face significant risks of recurrence, excess mortality, and diminished quality-of-life.

Early-stage NSCLC (eNSCLC) encompassing stage I and II, and resectable stage III disease is initially managed with curative-intent surgery and adjuvant chemotherapy to reduce the risk of recurrence. However, understanding the true curative potential and long-term outcomes is crucial for optimal clinical management. A literature review was conducted to identify observational studies describing long-term survival and quality-of-life outcomes following curative intent therapy in patients with eNSCLC. The proportion of patients who remained disease-free over time (without recurrence or death) statistically significantly decreased in patients with stage III disease compared with stage I disease. Similarly, the proportion of patients who remained recurrence-free over time decreased with increasing age and disease stage. A considerable risk of late recurrence (recurrence five or more years following resection) remained, increasing with advanced stage and tumor characteristics such as vascular invasion. Conditional 5-year relative survival rates did not exceed 87% in any study, indicating higher rates of all-cause mortality in long-term survivors of eNSCLC compared with members of the general population of the same age. Lower conditional 5-year relative survival rates, and 5 and 10-year relative survival rates were associated with older age and higher pathologic stage. Compared with the general population, survivors of eNSCLC reported significantly poorer physical quality-of-life, suggesting that symptoms persist after treatment. Overall, real-world evidence suggests that after standard curative-intent therapy, survivors of eNSCLC may not be considered fully cured, indicating a need for more effective adjuvant treatment in addition to the current standard of care.

The socioeconomic impact of disability progression in multiple sclerosis: A retrospective cohort study of the German NeuroTransData (NTD) registry.

Background: Multiple sclerosis (MS) is a progressively debilitating neurologic disease that poses significant costs to the healthcare system and workforce. Objective: To evaluate the impact of MS disease progression on societal costs and quality of life (QoL) using data from the German NeuroTransData (NTD) MS registry. Methods: Cross-sectional cohort study. The cost cohort included patients with MS disability assessed using Expanded Disability Status Scale (EDSS) in 2019 while the QoL cohort included patients assessed using EDSS and EuroQol-5 Dimension 5-Levels between 2009 and 2019. Direct and indirect medical, and non-medical resource use was quantified and costs derived from public sources. Results: Within the QoL cohort (n = 9821), QoL worsened with increasing EDSS. Within the cost cohort (n = 7286), increasing resource use with increasing EDSS was observed. Societal costs per patient, excluding or including disease-modifying therapies, increased from €5694 or €19,315 at EDSS 0 to 3.5 to €25,419 or €36,499 at EDSS 4 to 6.5, and €52,883 or €58,576 at EDSS 7 to 9.5. In multivariate modeling, each 0.5-step increase in EDSS was significantly associated with increasing costs, and worsening QoL. Conclusion: This study confirms the major socioeconomic burden associated with MS disability progression. From a socioeconomic perspective, delaying disability progression may benefit patients and society.

Treatment patterns and survival of patients with locoregional recurrence in early-stage NSCLC: a literature review of real-world evidence.

Approximately 10-50% of patients treated for early-stage (I-III), resectable non-small cell lung cancer (eNSCLC) will develop locoregional recurrence. There is a lack of prospective trials evaluating optimal post-surgery follow-up for this patient population, and treatment guidelines recommend salvage therapies such as surgery, local ablative therapy, and (chemo)radiotherapy. A literature review was conducted according to pre-defined criteria to identify observational studies describing treatment patterns and survival outcomes in patients with eNSCLC who experienced locoregional recurrence. Results showed that, in real-world clinical practice, around 80% of patients with locoregional recurrence underwent any form of active treatment. The most frequently administered treatments were chemotherapy (35.7%), chemoradiotherapy (31.2%), radiotherapy (20.3%), and surgery alone (12.8%). Chemoradiotherapy was associated with improved PFS and OS compared with radiotherapy, while no statistically significant survival benefits were observed for patients receiving surgery in addition to these treatments. The overall survival of patients following treatment for locoregional recurrence was generally poor, and the proportion of patients who experienced any form of post-treatment re-recurrence ranged from 35 to 72%. These findings highlight the need to develop more effective treatment strategies for locoregional recurrence, including preventative treatments, and strategies to improve the survival outcomes of those who do develop locoregional recurrence.

Dual Inhibition of PDK1 and Aurora Kinase A: An Effective Strategy to Induce Differentiation and Apoptosis of Human Glioblastoma Multiforme Stem Cells.

The poor prognosis of glioblastoma multiforme (GBM) is mainly attributed to drug resistance mechanisms and to the existence of a subpopulation of glioma stem cells (GSCs). Multitarget compounds able to both affect different deregulated pathways and the GSC subpopulation could escape tumor resistance and, most importantly, eradicate the stem cell reservoir. In this respect, the simultaneous inhibition of phosphoinositide-dependent kinase-1 (PDK1) and aurora kinase A (AurA), each one playing a pivotal role in cellular survival/migration/differentiation, could represent an innovative strategy to overcome GBM resistance and recurrence. Herein, the cross-talk between these pathways was investigated, using the single-target reference compounds MP7 (PDK1 inhibitor) and Alisertib (AurA inhibitor). Furthermore, a new ligand, SA16, was identified for its ability to inhibit the PDK1 and the AurA pathways at once, thus proving to be a useful tool for the simultaneous inhibition of the two kinases. SA16 blocked GBM cell proliferation, reduced tumor invasiveness, and triggered cellular apoptosis. Most importantly, the AurA/PDK1 blocker showed an increased efficacy against GSCs, inducing their differentiation and apoptosis. To the best of our knowledge, this is the first report on combined targeting of PDK1 and AurA. This drug represents an attractive multitarget lead scaffold for the development of new potential treatments for GBM and GSCs.

Best Matching Protein Conformations and Docking Programs for a Virtual Screening Campaign Against SMO Receptor.

SMO receptor is one of the main components of the Hedgehog biochemical pathway. In the last decades compelling body of evidence demonstrated that this receptor is a pertinent target for the treatment of various types of solid tumors. Recently, the X-ray determination of the three-dimensional structure of SMO in complex with different antagonists opened up the way for the structure-based design of new antagonists for this receptor that could possibly overcome the limitations connected with the induction of acquired tumor resistance. Herein, taking advantage of three different docking software (namely Glide, PLANTS, and Vina) and of the available SMO structures we set up a retrospective virtual screening (VS) protocol. A database, made up by known SMO antagonists and compounds with no alleged activity against the receptor was created and screened against the different SMO structures. To evaluate the performance of the ranking in VS calculations different statistical metrics (EF, AUAC and BEDROC) were employed allowing to identify the best performing VS docking protocol. Results of these studies will serve as a platform for the application of structure-based VS against the pharmaceutically relevant SMO receptor.

Locking PDK1 in DFG-out conformation through 2-oxo-indole containing molecules: Another tools to fight glioblastoma.

The phosphoinositide-dependent kinase-1 (PDK1) is one of the main components of the PI3K/Akt pathway. Also named the "master kinase" of the AGC family, PDK1 plays a critical role in tumorigenesis, by enhancing cell proliferation and inhibiting apoptosis, as well as in cell invasion and metastasis formation. Although there have been done huge efforts in discovering specific compounds targeting PDK1, nowadays no PDK1 inhibitor has yet entered the clinic. With the aim to pick out novel and potent PDK1 inhibitors, herein we report the design and synthesis of a new class of molecules obtained by merging the 2-oxo-indole nucleus with the 2-oxo-pyridonyl fragment, two moieties with high affinity for the PDK1 hinge region and its DFG-out binding site, respectively. To this purpose, a small series of compounds were synthesised and a tandem application of docking and Molecular Dynamic (MD) was employed to get insight into their mode of binding. The OXID-pyridonyl hybrid 8, possessing the lower IC50 (IC50 = 112 nM), was also tested against recombinant kinases involved in the PI3K/PDK1/Akt pathway and was subjected to vitro studies to evaluate the cytotoxicity and the inhibition of tumour cell migration. All together the results let us to consider 8, as a lead compound of a new generation of PDK1 inhibitors and encourage us to further studies in this direction.

Pathways and Barriers for Ion Translocation through the 5-HT3A Receptor Channel.

Pentameric ligand gated ion channels (pLGICs) are ionotropic receptors that mediate fast intercellular communications at synaptic level and include either cation selective (e.g., nAChR and 5-HT3) or anion selective (e.g., GlyR, GABAA and GluCl) membrane channels. Among others, 5-HT3 is one of the most studied members, since its first cloning back in 1991, and a large number of studies have successfully pinpointed protein residues critical for its activation and channel gating. In addition, 5-HT3 is also the target of a few pharmacological treatments due to the demonstrated benefits of its modulation in clinical trials. Nonetheless, a detailed molecular analysis of important protein features, such as the origin of its ion selectivity and the rather low conductance as compared to other channel homologues, has been unfeasible until the recent crystallization of the mouse 5-HT3A receptor. Here, we present extended molecular dynamics simulations and free energy calculations of the whole 5-HT3A protein with the aim of better understanding its ion transport properties, such as the pathways for ion permeation into the receptor body and the complex nature of the selectivity filter. Our investigation unravels previously unpredicted structural features of the 5-HT3A receptor, such as the existence of alternative intersubunit pathways for ion translocation at the interface between the extracellular and the transmembrane domains, in addition to the one along the channel main axis. Moreover, our study offers a molecular interpretation of the role played by an arginine triplet located in the intracellular domain on determining the characteristic low conductance of the 5-HT3A receptor, as evidenced in previous experiments. In view of these results, possible implications on other members of the superfamily are suggested.

Breaking the hydrophobicity of the MscL pore: insights into a charge-induced gating mechanism.

The mechanosensitive channel of large conductance (MscL) is a protein that responds to membrane tension by opening a transient pore during osmotic downshock. Due to its large pore size and functional reconstitution into lipid membranes, MscL has been proposed as a promising artificial nanovalve suitable for biotechnological applications. For example, site-specific mutations and tailored chemical modifications have shown how MscL channel gating can be triggered in the absence of tension by introducing charged residues at the hydrophobic pore level. Recently, engineered MscL proteins responsive to stimuli like pH or light have been reported. Inspired by experiments, we present a thorough computational study aiming at describing, with atomistic detail, the artificial gating mechanism and the molecular transport properties of a light-actuated bacterial MscL channel, in which a charge-induced gating mechanism has been enabled through the selective cleavage of photo-sensitive alkylating agents. Properties such as structural transitions, pore dimension, ion flux and selectivity have been carefully analyzed. Besides, the effects of charge on alternative sites of the channel with respect to those already reported have been addressed. Overall, our results provide useful molecular insights into the structural events accompanying the engineered MscL channel gating and the interplay of electrostatic effects, channel opening and permeation properties. In addition, we describe how the experimentally observed ionic current in a single-subunit charged MscL mutant is obtained through a hydrophobicity breaking mechanism involving an asymmetric inter-subunit motion.