Mobile Mechanism Research Articles

Suppression by Mobilization: How Information Control Strategies Contain Political Criticism in Autocracies

Autocrats selectively tolerate political criticism, which may erode regime support. The literature suggests that regimes contain criticism by encouraging more supportive voices, but the mechanisms remain unclear. We theorize two mechanisms: winning more supporters (persuasion) or mobilizing existing supporters to speak out (mobilization). These mechanisms can be created by censoring evidence that supports criticism and adopting propaganda to arouse nationalism or promise material gains. We conducted two survey experiments in China with a novel measurement of supporter mobilization: respondents’ written defenses against criticism. We find evidence of a mobilization mechanism but not persuasion. Censoring facts strongly encourages supportive comments. Ideological propaganda’s effects are moderate, whereas propaganda on material benefits has no effect.

Source of arsenic pollution in southern Indus alluvial plain aquifers, Pakistan

Aquifers in Indus alluvial plain are naturally polluted by arsenic (As). Millions of population in Pakistan use groundwater for drinking is exposed to As ingested diseases. Present investigations were focused on the mobilization mechanism of As in the alluvial aquifers, in Matiari district of Pakistan, which is mainly covered by alluvial sediments of Holocene and Pleistocene age. These sediments are weathered from Himalayas and its neighboring regions and are primarily deposited by Indus River. About 94 samples of groundwater were collected from various localities of Matiari district. Physico-chemical data revealed that 60% of wells exceed 10 μg/L, WHO permissible standard for drinking water. Low nitrate and neutral to near neutral pH and negative Eh in most of the wells are indicative of reducing conditions in the aquifers. Ancient courses of Indus river and domestic and agricultural wastes could be an important source of organic matter. Microbiodegradation of organic matter has created reducing conditions in the aquifer, which trigger the reduction of sedimentary iron oxyhydroxides and the mobilize As in shallow aquifers of Matiari. A borehole was also drilled to decipher the lithological and geochemical characteristics of aquifer material. Elemental, petrographic and SEM-EDS data revealed that sediments are comprised of brown aquitard clay and well sorted grey fine sand. Arsenic in sand and clay samples ranged between 0.8 and 3.9 mg/kg and 0.3–3.2 mg/kg respectively. Dominant minerals in the aquifers sediments are phlogopite and biotite. Leaching of these minerals under reducing conditions is likely to provide higher concentration of As in the groundwater of the area.

Understanding the role of storage reserve mobilization during seed germination and initial seedling growth in species of the genus Carapa

A physiological and metabolic database for various species of Amazonian plants is crucial to the species selection and sustainable utilization of their diversity. We hypothesized that understanding the mobilization of Carapa seed reserves and water uptake during germination could provide insights into the physiological behavior and propagation to differentiate species of the same genus. Given this, the mobilization mechanisms of primary reserves, water uptake, and enzymatic activities in seeds of two species of Carapa (C. guianensis and C. vasquezii) were investigated. The lipid content was high in both species, with a value of 63.7±4.7% for C. guianensis and 55±1.5% for C. vasquezii. C. guianensis showed higher values for the other evaluated reserves. The protein profile highlights a band between 15 and 25 kDa in C. guianensis. As for the enzymatic activities investigated (lipase, amylase, protease, acid phosphatase), C. guianensis showed greater activity for most of them, except for acid phosphatase. Overall, the species showed different metabolic strategies and dynamics regarding the water uptake and use of reserves. Our findings indicate that distinct metabolic pathways are employed during the germination and initial seedling growth stages of two Carapa species. This trait can potentially guide the use and preservation of these species.

Posterior Semicircular Canal Dehiscence with Vestibulo-Ocular Reflex Reduction for the Affected Canal at the Video-Head Impulse Test: Considerations to Pathomechanisms.

Posterior semicircular canal dehiscence (PSCD) has been demonstrated to result in a third mobile window mechanism (TMWM) in the inner ear similar to superior semicircular canal dehiscence (SSCD). Typical clinical and instrumental features of TMWM, including low-frequency conductive hearing loss (CHL), autophony, pulsatile tinnitus, sound/pressure-induced vertigo and enhanced vestibular-evoked myogenic potentials, have been widely described in cases with PSCD. Nevertheless, video-head impulse test (vHIT) results have been poorly investigated. Here, we present six patients with PSCD presenting with a clinical scenario consistent with a TMWM and an impaired vestibulo-ocular reflex (VOR) for the affected canal on vHIT. In two cases, an additional dehiscence between the facial nerve and the horizontal semicircular canal (HSC) was detected, leading to a concurrent VOR impairment for the HSC. While in SSCD, a VOR gain reduction could be ascribed to a spontaneous "auto-plugging" process due to a dural prolapse into the canal, the same pathomechanism is difficult to conceive in PSCD due to a different anatomical position, making a dural herniation less likely. Alternative putative pathomechanisms are discussed, including an endolymphatic flow dissipation during head impulses as already hypothesized in SSCD. The association of symptoms/signs consistent with TMWM and a reduced VOR gain for the posterior canal might address the diagnosis toward PSCD.

Novel insights into phage biology of the pathogen Clostridioides difficile based on the active virome.

The global pathogen Clostridioides difficile is a well-studied organism, and researchers work on unraveling its fundamental virulence mechanisms and biology. Prophages have been demonstrated to influence C. difficile toxin expression and contribute to the distribution of advantageous genes. All these underline the importance of prophages in C. difficile virulence. Although several C. difficile prophages were sequenced and characterized, investigations on the entire active virome of a strain are still missing. Phages were mainly isolated after mitomycin C-induction, which does not resemble a natural stressor for C. difficile. We examined active prophages from different C. difficile strains after cultivation in the absence of mitomycin C by sequencing and characterization of particle-protected DNA. Phage particles were collected after standard cultivation, or after cultivation in the presence of the secondary bile salt deoxycholate (DCA). DCA is a natural stressor for C. difficile and a potential prophage-inducing agent. We also investigated differences in prophage activity between clinical and non-clinical C. difficile strains. Our experiments demonstrated that spontaneous prophage release is common in C. difficile and that DCA presence induces prophages. Fourteen different, active phages were identified by this experimental procedure. We could not identify a definitive connection between clinical background and phage activity. However, one phage exhibited distinctively higher activity upon DCA induction in the clinical strain than in the corresponding non-clinical strain, although the phage is identical in both strains. We recorded that enveloped DNA mapped to genome regions with characteristics of mobile genetic elements other than prophages. This pointed to mechanisms of DNA mobility that are not well-studied in C. difficile so far. We also detected phage-mediated lateral transduction of bacterial DNA, which is the first described case in C. difficile. This study significantly contributes to our knowledge of prophage activity in C. difficile and reveals novel aspects of C. difficile (phage) biology.

First report of multidrug-resistant carbapenemase-producing Aeromonas caviae co-harboring mcr-3.43 and mcr-7.2.

Hospital sewage serves as a crucial reservoir for antibiotic resistance genes. As colistin and carbapenems are the last-resort antibiotics, the emergence of their resistance genes has become a significant concern in clinical settings. In this study, we found that two novel mcr alleles (mcr-3.43 and mcr-7.2) with two carbapenemase genes (blaNDM-1 and blaKPC-2) were encoded in a single Aeromonas caviae strain isolated from hospital sewage. Our phylogenetic analysis revealed that the mcr-3.43 gene clustered with mcr-3.17 (with 95.55% amino acid identity), while the mcr-7.2 gene clustered with mcr-7.1 (with 68.68% amino acid identity). BLAST search against GenBank showed that mcr-7.2 was exclusively detected in Aeromonas spp. Mobile genetic elements were not found in the genetic context of mcr-7.2, suggesting that the dissemination of mcr-7.2 in Aeromonas spp. may be dependent on vertical transfer or recombination. The blaNDM-1 was adjacent to a recombinase gene and flanked by two IS91 elements, indicating a potential mobilization mechanism mediated by recombination and/or ISs. The blaKPC-2 gene was located on an IncU plasmid and adjacent to an ISKpn6. In summary, our study provides evidence for Aeromonas spp. as one of the potential reservoirs of colistin and carbapenem resistance genes.IMPORTANCEThe study discovered two novel mcr genes (mcr-3.43 and mcr-7.2) and two carbapenemase genes (blaNDM-1 and blaKPC-2) in a single Aeromonas caviae strain retrieved from hospital sewage. Using phylogenetic analysis and comparative data evaluation, the study revealed the genetic relatedness and dissemination potential of the detected resistance genes. With the exclusive discovery that mcr-7.2 is only present in Aeromonas spp. and the lack of mobile genetic elements in its genetic context, there is a strong indication of limited dissemination. The identification of these four resistance genes in a single strain of Aeromonas provided valuable insights into their potential presence in this genus. This study revealed that hospital sewage functions as a significant reservoir for antibiotic resistance genes, including colistin and carbapenem resistance genes.

Mobile medial pivot (lateral slide)-type total knee arthroplasty exhibited different motion patterns between under anaesthesia and weight-bearing condition.

Total knee arthroplasty (TKA), which has medial pivot and mobile-bearing mechanisms, has been developed and clinically used. However, the in vivo dynamic kinematics of the mobile medial pivot-type TKA (MMPTKA) is unclear. This study analysed the in vivo kinematics of MMPTKA in weight-bearing and nonweight-bearing conditions. The study included 10 knees that underwent primary TKA using MMPTKA. After TKA, lateral view radiographs of the knee in full extension, 90° of flexionand passive full flexion were taken under general anaesthesia in the nonweight-bearing condition. At least 6 months postoperatively, knee motion during squatting from a weight-bearing standing position was observed using a flat-panel detector and analysed using the three-dimensional-to-two-dimensional image registration technique. Under anaesthesia: in passive full flexion, the anteroposterior (AP) locations of the femoral component's medial and lateral distal points were 10.2 and 16.0 mm posterior, and the rotational angles of the femoral component's X-axis (FCX) and insert were 8.1° external rotation and 18.5° internal rotation to full extension, respectively. Squatting: the AP translations of the femoral component's medial and lateral most distal points were 2.2 and 6.4 mm, and the rotational angles of the FCX and insert were 5.7° and 1.6° external rotation, respectively. Significant differences were observed in the AP translation of the femoral component's medial and lateral most distal points and changes in the insert's rotational angle when comparing under anaesthesia and squatting. The kinematics of the insert in MMPTKA was significantly influenced by loading and muscle contraction. The femoral component exhibited substantial external rotation and posterior translation under anaesthesia, which may contribute to achieving an optimal range of motion. The insert remained relatively stable during squatting and minimal rotation was observed, indicating good stability. MMPTKA was expected to demonstrate rational kinematics by incorporating mobile and medial pivot mechanisms. Level IV,prospective biomechanical case series study.

U.S. mobilization of its domestic diaspora: Strategic leveraging of an un[der]tapped foreign policy resource

AbstractThe historic diaspora diplomacy literature has generally characterized politically active diaspora as foreign agents leveraged by their ancestral homeland to shape the foreign policy of their host nation. As such, diaspora groups have generally been assessed as net negatives on the foreign policy of their host nations, or as working against the common good of the host nation. This work seeks to challenge this narrow conceptualization and demonstrate that, when considered within a broader historical timeline, granted agency, and contextualized within a networked society, emergent mechanisms for state mobilization of diaspora groups to achieve foreign policy objectives become apparent. This work is focused exclusively on political diaspora groups within the United States and investigates select case studies to demonstrate the evolving nature of U.S.–diaspora relations and the opportunities presented as a result. The work concludes with several policy recommendations, derived from lessons learned within the case studies.Related ArticlesBayes, Jane H., and Laura Gonzalez. 2011. “Globalization, Transnationalism, and Intersecting Geographies of Power: The Case of the Consejo Consultivo del Instituto de los Mexicanos en el Exterior (CC‐IME): A Study in Progress.” Politics & Policy 39(1): 11–44. https://doi.org/10.1111/j.1747‐1346.2010.00281.x.Huijgh, Ellen. 2017. “Indonesia's ‘Intermestic’ Public Diplomacy: Features and Future.” Politics & Policy 45(5): 762–92. https://doi.org/10.1111/polp.12221.Singh, Amit, and Amit Sarwal. 2017. “Paraspara, Encounters, and Confluences: India's Soft Power Objective in the Indo‐Pacific Region.” Politics & Policy 45(5): 733–61. https://doi.org/10.1111/polp.12222.

Distinct and overlapping RNA determinants for binding and target-primed reverse transcription by Bombyx mori R2 retrotransposon protein.

Eukaryotic retrotransposons encode a reverse transcriptase that binds RNA to template DNA synthesis. The ancestral non-long terminal repeat (non-LTR) retrotransposons encode a protein that performs target-primed reverse transcription (TPRT), in which the nicked genomic target site initiates complementary DNA (cDNA)synthesis directly into the genome. The best understood model system for biochemical studies of TPRT is the R2 protein from the silk moth Bombyx mori. The R2 protein selectively binds the 3' untranslated region of its encoding RNA as template for DNA insertion to its target site in 28S ribosomal DNA. Here, binding and TPRT assays define RNA contributions to RNA-protein interaction, template use for TPRT and the fidelity of template positioning for TPRT cDNA synthesis. We quantify both sequence and structure contributions to protein-RNA interaction. RNA determinants of binding affinity overlap but are not equivalent to RNA features required for TPRT and its fidelity of template positioning for full-length TPRT cDNA synthesis. Additionally, we show that a previously implicated RNA-binding protein surface of R2 protein makes RNA binding affinity dependent on the presence of two stem-loops. Our findings inform evolutionary relationships across R2 retrotransposon RNAs and are a step toward understanding the mechanism and template specificity of non-LTR retrotransposon mobility.

Effect of temperature modulation on the performance of top contact bottom gate organic thin film transistor

This research article investigates the influence of temperature variations on the performance parameters of Top Contact Bottom Gate (TCBG) Organic Thin Film Transistors (OTFTs). Employing the Arrhenius equation and Schottky emission model, the study explores temperature-dependent charge carrier mobility and injection mechanisms. Analyzing a wide range of parameters, the research unveils a complex interplay between temperature and OTFT behavior. The linear and saturation mobilities exhibit a decline due to enhanced carrier-phonon interactions and lattice vibrations. Transconductance and ION/IOFF ratio display a concomitant decrease at higher temperatures, indicative of the heightened susceptibility of OTFT performance to temperature fluctuations. The depreciation in subthreshold slope and threshold voltage with rising temperatures underscores the influence of temperature on trap states. The research emphasizes the importance of considering temperature’s impact during OTFT design for diverse applications, enhancing the reliability and functionality of organic electronic devices.

Fuzzy evaluation model for physical education teaching methods in colleges and universities using artificial intelligence.

The evaluation of Physical Education Teaching Methods in Colleges and Universities faces two main challenges: an excess of evaluating elements and a lack of assessment framework. Hence, the research proposes the multi-feature fuzzy evaluation model based on artificial intelligence to streamline the evaluation process and provide an efficient framework for accessing teaching methods. The framework integrates natural/human language using fuzzy instructions considering three evaluation perspectives, including the management stage, instructors, and students and employs the enhanced cuckoo search optimization algorithm. After the teaching expert has determined each parameter's ratings, they are fed into the improved cuckoo search algorithm and solved using an unbiased function to assess the assessment's final result. It incorporates the students' mobility mechanism and movement vector deconstruction designed based on functional criteria. A system for evaluating the quality of instruction has been developed utilizing the proposed model with enhanced cuckoo search optimization. The results indicate that the proposed algorithm has achieved the highest scores across multiple assessment categories, average skill performances of 97.01%, learning progress of 87.36%, physical fitness of 93.49%, participation rate of 95.04%, student satisfaction of 95.49%, and physical education of 96.8% teaching efficiency. The usefulness of the proposed framework in enhancing physical education teaching methods has been demonstrated by comparing the results with traditional methods. It contributes to advancing pedagogical practices in the field.

Influence of Electrode Potential on Oxygen Mobility Probed by Polarized Isotopic Exchange in Solid Oxide Electrolyser Cells: Insights for Electro‐Assisted Oxidation Reactions

AbstractOxygen mobility was studied by oxygen isotopic exchange on three electrodes used in Solid Oxide Electrolyser Cells under polarization (La0.8Sr0.2MnO3 (LSM), La0.6Sr0.4Co0.2Fe0.8O3‐δ (LSCF) and La2NiO4+δ (LNO)). The rate of the surface and the bulk mechanisms for oxygen mobility is depending on the type of conductivity (electronic conduction or mixed ionic and electronic conductivity). It is shown that a one oxygen atom exchange is dominant for the surface path whereas a two oxygen atoms mechanism dominates for the bulk path. The rate constant for the bulk path is much higher than the one for the surface path by two orders of magnitude. Additionally, polarized oxygen isotopic exchange revealed that electrode overvoltage increases significantly the rate constant for the surface path, whereas its impact on the bulk path is negligible.

Revolutionary leaders and the punishment of critics

I explore a previously neglected mechanism of mass mobilization in autocracies. Revolutionary leaders may deliberately provoke punishment from the incumbent regime to signal their political conviction and thus encourage citizens to identify with and support the revolutionary movement. I model the interplay of repression, criticism, and revolutionary actions as a dynamic game with incomplete information about the leader’s type. The role of the revolutionary leader is to enable people to identify with the movement by credibly embodying political change. From the incumbent’s perspective, repression turns out to be a double-edged sword. On the one hand, a severe punishment of critics increases citizens’ cost of participating in revolutionary actions. On the other hand, harsh repressions may simultaneously establish a trustworthy leader whom people want to follow in order to replace the current political regime. My results thus help explain a stylized fact, namely that revolutionary leaders sometimes need to fail before they can succeed.

Role of microstructure in the exploitation of self-healing potential in form-stable composite phase change materials based on immiscible alloys

Metallic Phase Change Materials (PCMs), based on solid-liquid transitions, represents one of the most promising technologies for efficient Thermal Energy Storage (TES), due to their superior thermal conductivity and energy storability per unit volume, but suffer of limited solutions for their handling at the molten state. The use of Miscibility Gap Alloys (MGAs) allows to manage PCM volume expansion and keep it confined when molten, preventing interaction with the environment. A relevant example is provided by the Al-Sn system, where Al covers the role of the high-temperature stable and highly thermal-conductive passive matrix and Sn the active PCM. The alloy can thus be considered a Composite PCM (C-PCM). The response fastness of these systems depends on their thermal diffusivity, subjected to abrupt variations under the presence of discontinuities and damages. In this sense, the authors investigated the possibility to employ molten Sn mobility in a potentially damaged C-PCM for self-healing purposes, aimed to restore, at least partially, the material continuity and thus its thermal diffusivity. Exudation heat treatments above the melting temperature of Sn were performed on sets of Al-40%wt. Sn metallic composites, produced either with powder metallurgy or liquid metal routes, in order to quantify and assess the mobility of the Sn under simulated operating conditions. Exudation tests assess Simple Mixed powders and liquid metal routes sample as the ones with the highest healing potential. Al dissolution and re-deposition was established by EDS analyses as one of the principal Sn mobility mechanisms. Laser Flash Analysis tests, as well as microstructural investigations, were performed on the samples before and after both healing-focused and simulated service heat treatments to evaluate the changes of thermal diffusivity. Healing-focused treatment at 250°C for 1 hour generally displayed a moderate thermal diffusivity recovery and simulated service by shorter cycles between 170°C and 270°C slightly reduce it. The beneficial role of healing focused heat treatments at 250°C for 1 hour suggests that the presence of fully molten Sn phase during service for relatively long time could be beneficial for functional healing. The requirements of suitable Al-Sn microstructures for self-healing purposes, granting at the same time the C-PCM functionalities, i.e., thermal energy storage and form-stability, were set.

Transnational cultural networks: soft mechanisms for cultural diversity and frictionless mobility

ABSTRACT Transnational networks in the cultural sector have expanded significantly in Europe over the last three decades. Nevertheless, although this phenomenon is fuelled by the EU’s cultural policy and corresponding funding initiatives, there is a noticeable lacuna in the academic literature on this issue. This article, therefore, examines the emergence and institutionalisation of these networks, shedding light on: 1) the relationship between networks’ evolution and the EU’s cultural policy discourse, and 2) networks and the Europeanisation process. To this end, the study employs a document analysis and uncovers three distinct policy clusters, with a shift from a transnational European identity to one of cultural diversity and a people-centered approach. These outcomes lead to an investigation of whether and how these discursive shifts are interconnected with the development of transnational networks. This conclusively reveals how their implementation is intricately linked not only to the foundational tenets of the EU’s cultural policy – the subsidiarity principle, but also to the broader context of EU policymaking. The article concludes that EU intervention in the cultural sector can be justified as a discursive agent in the evolving European public sphere, with significant implications for professionals, policymakers and scholars in the field.

Antimony mobility in soil near historical waste rock at the world's largest Sb mine, Central China

Soil near waste rock often contains high concentrations of antimony (Sb), but the mechanisms that mobilize Sb in a soil closely impacted by the waste rock piles are not well understood. We investigated these mobility mechanisms in soils near historical waste rock at the world's largest Sb mine. The sequential extraction (BCR) of soil reveal that over 95 % Sb is present in the residual fraction. The leached Sb concentration is related to the surface protonation and deprotonation of soil minerals. SEM-EDS shows Sb in the soil is associated with Fe and Ca. Moreover, X-ray absorption spectroscopy (XAS) results show Sb is predominantly present as Sb(V) and is associated with Fe in the form of tripuhyite (FeSbO4) as well as edge- and corner-sharing complexes on ferrihydrite and goethite. Thus, Fe in soils is important in controlling the mobility of Sb via surface complexation and co-precipitation of Sb by Fe oxides. The initially surface-adsorbed Sb(V) or co-precipitation is likely to undergo a phase transformation as the Fe oxides age. In addition, Sb mobility may be controlled by small amounts of calcium antimonate. These results further the understanding of the effect of secondary minerals in soils on the fate of Sb from waste rock weathering and inform source treatment for Sb-contaminated soils.

Spatial Distribution, Ecological Risk Assessment, and Source Identification of Metals in Sediments of the Krka River Estuary (Croatia)

To evaluate the level of contamination and predict the potential toxicity risk, selected metal concentrations (Cd, Pb, Cr, Mn, Co, Ni, Cu, Zn, and As) were determined in 40 surface sediment samples from the stratified karstic Krka River estuary (Croatia). In addition, diffusive gradients in thin films (DGT) probes were deployed in situ to understand the mobilization mechanisms and bioavailability of metals in the sediment. The results show significant spatial differences between the upper and lower estuary, with the latter being more affected by anthropogenic pollution. The pollution assessment using the enrichment factor (EF), the geoaccumulation index (Igeo), and the pollution load index (PLI) showed a strong enrichment of metals in the lower part of the estuary, especially of Mn, Cu, Zn, Pb, and As. The statistical analysis (PCA) revealed the former ferromanganese factory and the port as major sources of pollution in the area. Nickel, Co, and Cr, although slightly elevated, may be attributed to the natural origin. The metal mobility in the estuarine sediment was primarily governed by early diagenetic processes (aerobic organic matter mineralization, Fe and Mn oxyhydroxide reduction), which caused the release of metals from the sediment into the pore water and subsequently into the overlying water column.

The political economy of economic upgrading in Central Eastern Europe

ABSTRACT The paper explores the political conditions favourable to economic upgrading in democratic non-corporatist emerging economies with a focus on CEE countries as characteristic examples. While the existing literature has assumed this polity type to be the least favourable for designing and implementing effective industrial policies because of a lack of bureaucratic ‘embedded autonomy’, the paper argues that this is not to suggest that such industrial policies and economic upgrading are rare in these economies, but rather that they involve different mechanisms of political mobilisation and support. To identify these mechanisms, the paper adopts a social bloc-based framework and applies it to an in-depth study of Estonia, a strong upgrader in the region in terms of its increased economic specialisation in ICT-based services. The paper finds that a lack of ‘embedded autonomy’ can effectively be supplanted by the embeddedness of private actors in the state administration and political decision-making through a network-based configuration of the social bloc and a shared upgrading ideology leading to a conflation of private interests with national development goals.

Mobile barrier mechanisms for Na+-coupled symport in an MFS sugar transporter

While many 3D structures of cation-coupled transporters have been determined, the mechanistic details governing the obligatory coupling and functional regulations still remain elusive. The bacterial melibiose transporter (MelB) is a prototype of major facilitator superfamily transporters. With a conformation-selective nanobody, we determined a low-sugar affinity inward-facing Na+-bound cryoEM structure. The available outward-facing sugar-bound structures showed that the N- and C-terminal residues of the inner barrier contribute to the sugar selectivity. The inward-open conformation shows that the sugar selectivity pocket is also broken when the inner barrier is broken. Isothermal titration calorimetry measurements revealed that this inward-facing conformation trapped by this nanobody exhibited a greatly decreased sugar-binding affinity, suggesting the mechanisms for substrate intracellular release and accumulation. While the inner/outer barrier shift directly regulates the sugar-binding affinity, it has little or no effect on the cation binding, which is supported by molecular dynamics simulations. Furthermore, the hydron/deuterium exchange mass spectrometry analyses allowed us to identify dynamic regions; some regions are involved in the functionally important inner barrier-specific salt-bridge network, which indicates their critical roles in the barrier switching mechanisms for transport. These complementary results provided structural and dynamic insights into the mobile barrier mechanism for cation-coupled symport.

Mobile barrier mechanisms for Na+-coupled symport in an MFS sugar transporter.

While many 3D structures of cation-coupled transporters have been determined, the mechanistic details governing the obligatory coupling and functional regulations still remain elusive. The bacterial melibiose transporter (MelB) is a prototype of major facilitator superfamily transporters. With a conformation-selective nanobody, we determined a low-sugar affinity inward-facing Na+-bound cryoEM structure. The available outward-facing sugar-bound structures showed that the N- and C-terminal residues of the inner barrier contribute to the sugar selectivity. The inward-open conformation shows that the sugar selectivity pocket is also broken when the inner barrier is broken. Isothermal titration calorimetry measurements revealed that this inward-facing conformation trapped by this nanobody exhibited a greatly decreased sugar-binding affinity, suggesting the mechanisms for substrate intracellular release and accumulation. While the inner/outer barrier shift directly regulates the sugar-binding affinity, it has little or no effect on the cation binding, which is supported by molecular dynamics simulations. Furthermore, the hydron/deuterium exchange mass spectrometry analyses allowed us to identify dynamic regions; some regions are involved in the functionally important inner barrier-specific salt-bridge network, which indicates their critical roles in the barrier switching mechanisms for transport. These complementary results provided structural and dynamic insights into the mobile barrier mechanism for cation-coupled symport.