Engineering 2D Material Exciton Line Shape with Graphene/h-BN Encapsulation.

Control over the optical properties of atomically thin two-dimensional (2D) layers, including those of transition metal dichalcogenides (TMDs), is needed for future optoelectronic applications. Here, the near-field coupling between TMDs and graphene/graphite is used to engineer the exciton line shape and charge state. Fano-like asymmetric spectral features are produced in WS2, MoSe2, and WSe2 van der Waals heterostructures combined with graphene, graphite, or jointly with hexagonal boron nitride (h-BN) as supporting or encapsulating layers. Furthermore, trion emission is suppressed in h-BN encapsulated WSe2/graphene with a neutral exciton red shift (44 meV) and binding energy reduction (30 meV). The response of these systems to electron beam and light probes is well-described in terms of 2D optical conductivities of the involved materials. Beyond fundamental insights into the interaction of TMD excitons with structured environments, this study opens an unexplored avenue toward shaping the spectral profile of narrow optical modes for application in nanophotonic devices.

Mediation of Successful Reperfusion Effect through Infarct Growth and Cerebral Edema: A Pooled, Patient-Level Analysis of EXTEND-IA Trials and SELECT Prospective Cohort.

OBJECTIVE: Reperfusion therapy is highly beneficial for ischemic stroke. Reduction in both infarct growth and edema are plausible mediators of clinical benefit with reperfusion. We aimed to quantify these mediators and their interrelationship. METHODS: In a pooled, patient-level analysis of the EXTEND-IA trials and SELECT study, we used a mediation analysis framework to quantify infarct growth and cerebral edema (midline shift) mediation effect on successful reperfusion (modified Treatment in Cerebral Ischemia ≥ 2b) association with functional outcome (modified Rankin Scale distribution). Furthermore, we evaluated an additional pathway to the original hypothesis, where infarct growth mediated successful reperfusion effect on midline shift. RESULTS: A total 542 of 665 (81.5%) eligible patients achieved successful reperfusion. Baseline clinical and imaging characteristics were largely similar between those achieving successful versus unsuccessful reperfusion. Median infarct growth was 12.3ml (interquartile range [IQR] = 1.8-48.4), and median midline shift was 0mm (IQR = 0-2.2). Of 249 (37%) demonstrating a midline shift of ≥1mm, median shift was 2.75mm (IQR = 1.89-4.21). Successful reperfusion was associated with reductions in both predefined mediators, infarct growth (ß = -1.19, 95% confidence interval [CI] = -1.51 to -0.88, p < 0.001) and midline shift (adjusted odds ratio = 0.36, 95% CI = 0.23-0.57, p < 0.001). Successful reperfusion association with improved functional outcome (adjusted common odds ratio [acOR] = 2.68, 95% CI = 1.86-3.88, p < 0.001) became insignificant (acOR = 1.39, 95% CI = 0.95-2.04, p = 0.094) when infarct growth and midline shift were added to the regression model. Infarct growth and midline shift explained 45% and 34% of successful reperfusion effect, respectively. Analysis considering an alternative hypothesis demonstrated consistent results. INTERPRETATION: In this mediation analysis from a pooled, patient-level cohort, a significant proportion (~80%) of successful reperfusion effect on functional outcome was mediated through reduction in infarct growth and cerebral edema. Further studies are required to confirm our findings, detect additional mediators to explain successful reperfusion residual effect, and identify novel therapeutic targets to further enhance reperfusion benefits. ANN NEUROL 2023;93:793-804.

Mycobacterium tuberculosis exploits MPT64 to generate myeloid-derived suppressor cells to evade the immune system.

Mycobacterium tuberculosis (Mtb) is a smart and successful pathogen since it can persist in the intimidating environment of the host by taming and tuning the immune system. Mtb releases MPT64 (Rv1980c) protein in high amounts in patients with active tuberculosis (TB). Consequently, we were curious to decipher the role of MPT64 on the differentiating dendritic cells (DCs) and its relation to evading the immune system. We observed that pre-exposure of differentiating DCs to MPT64 (DCMPT64) transformed them into a phenotype of myeloid-derived suppressor cells (MDSCs). DCMPT64 expressed a high level of immunosuppressive molecules PD-L1, TIM-3, nitric oxide (NO), arginase 1, IDO-1, IL-10 and TGF-ß, but inhibited the production of pro-inflammatory cytokines TNF-α, IL-6 and IL-12. DCMPT64 chemotaxis function was diminished due to the reduced expression of CCR7. DCMPT64 promoted the generation of regulatory T cells (Tregs) but inhibited the differentiation of Th1 cells and Th17 cells. Further, high lipid and methylglyoxal content, and reduced glucose consumption by DCMPT64, rendered them metabolically quiescent and consequently, reduced DCMPT64 ability to phagocytose Mtb and provided a safer shelter for the intracellular survival of the mycobacterium. The mechanism identified in impairing the function of DCMPT64 was through the increased production and accumulation of methylglyoxal. Hence, for the first time, we demonstrate the novel role of MPT64 in promoting the generation of MDSCs to favor Mtb survival and escape its destruction by the immune system.

Early Infarct Growth Rate Correlation With Endovascular Thrombectomy Clinical Outcomes: Analysis From the SELECT Study.

BACKGROUND AND PURPOSE: Time elapsed from last-known well (LKW) and baseline imaging results are influential on endovascular thrombectomy (EVT) outcomes. METHODS: In a prospective multicenter cohort study of imaging selection for endovascular thrombectomy (SELECT [Optimizing Patient's Selection for Endovascular Treatment in Acute Ischemic Stroke], the early infarct growth rate (EIGR) was defined as ischemic core volume on perfusion imaging (relative cerebral blood flow<30%) divided by the time from LKW to imaging. The optimal EIGR cutoff was identified by maximizing the sum of the sensitivity and specificity to correlate best with favorable outcome and to improve its the predictability. Patients were stratified into slow progressors if EIGR2. The primary outcome was 90-day functional independence (modified Rankin Scale score =0-2). RESULTS: Of 445 consented, 361 (285 EVT, 76 medical management only) patients met the study inclusion criteria. The optimal EIGR was <10 mL/h; 200 EVT patients were slow and 85 fast progressors. Fast progressors had a higher median National Institutes of Health Stroke Scale (19 versus 15, P<0.001), shorter time from LKW to groin puncture (180 versus 266 minutes, P<0.001). Slow progressors had better collaterals on computed tomography perfusion: hypoperfusion intensity ratio (adjusted odds ratio [aOR]: 5.11 [2.43-10.76], P<0.001) and computed tomography angiography: collaterals-score (aOR: 4.43 [1.83-10.73], P=0.001). EIGR independently correlated with functional independence after EVT, adjusting for age, National Institutes of Health Stroke Scale, time LKW to groin puncture, reperfusion (modified Thrombolysis in Cerebral Infarction score of ≥2b), IV-tPA (intravenous tissue-type plasminogen activator), and transfer status (aOR: 0.78 [0.65-0.94], P=0.01). Slow progressors had higher functional independence rates (121 [61%] versus 30 [35%], P<0.001) and had 3.5 times the likelihood of achieving modified Rankin Scale score =0-2 with EVT (aOR=2.94 [95% CI, 1.53-5.61], P=0.001) as compared to fast progressors, who had substantially worse clinical outcomes both in early and late time window. The odds of good outcome decreased by 14% for each 5 mL/h increase in EIGR (aOR, 0.87 [0.80-0.94], P<0.001) and declined more rapidly in fast progressors. CONCLUSIONS: The EIGR strongly correlates with both collateral status and clinical outcomes after EVT. Fast progressors demonstrated worse outcomes when receiving EVT beyond 6 hours of stroke onset as compared to those who received EVT within 6 hours. Registration: URL: https://clinicaltrials.gov. Unique identifier: NCT02446587.

Optimizing Patient Selection for Endovascular Treatment in Acute Ischemic Stroke (SELECT): A Prospective, Multicenter Cohort Study of Imaging Selection.

OBJECTIVE: The primary imaging modalities used to select patients for endovascular thrombectomy (EVT) are noncontrast computed tomography (CT) and CT perfusion (CTP). However, their relative utility is uncertain. We prospectively assessed CT and CTP concordance/discordance and correlated the imaging profiles on both with EVT treatment decisions and clinical outcomes. METHODS: A phase 2, multicenter, prospective cohort study of large-vessel occlusions presented up to 24 hours from last known well was conducted. Patients received a unified prespecified imaging evaluation (CT, CT angiography, and CTP with Rapid Processing of Perfusion and Diffusion software mismatch determination). The treatment decision, EVT versus medical management, was nonrandomized and at the treating physicians' discretion. An independent, blinded, neuroimaging core laboratory adjudicated favorable profiles based on predefined criteria (CT:Alberta Stroke Program Early CT Score ≥ 6, CTP:regional cerebral blood flow (<30%) < 70ml with mismatch ratio ≥ 1.2 and mismatch volume ≥ 10ml). RESULTS: Of 4,722 patients screened from January 2016 to February 2018, 361 patients were included. Two hundred eighty-five (79%) received EVT, of whom 87.0% had favorable CTs, 91% favorable CTPs, 81% both favorable profiles, 16% discordant, and 3% both unfavorable. Favorable profiles on the 2 modalities correlated similarly with 90-day functional independence rates (favorable CT = 56% vs favorable CTP = 57%, adjusted odds ratio [aOR] = 1.91, 95% confidence interval [CI] = 0.40-9.01, p = 0.41). Having a favorable profile on both modalities significantly increased the odds of receiving thrombectomy as compared to discordant profiles (aOR = 3.97, 95% CI = 1.97-8.01, p < 0.001). Fifty-eight percent of the patients with favorable profiles on both modalities achieved functional independence as compared to 38% in discordant profiles and 0% when both were unfavorable (p < 0.001 for trend). In favorable CT/unfavorable CTP profiles, EVT was associated with high symptomatic intracranial hemorrhage (sICH) (24%) and mortality (53%) rates. INTERPRETATION: Patients with favorable imaging profiles on both modalities had higher odds of receiving EVT and high functional independence rates. Patients with discordant profiles achieved reasonable functional independence rates, but those with an unfavorable CTP had higher adverse outcomes. Ann Neurol 2020;87:419-433.

Thrombolysis for stroke in elderly in the late window period.

OBJECTIVES: Safety of intravenous thrombolysis (IVT) within 3-4.5 hours of stroke onset in patients ≥80 years is still disputable. We evaluated the association of symptom onset-to-treatment time (SOTT) with the symptomatic intracranial hemorrhage (sICH), poor outcome, and mortality in patients≥80 years. MATERIALS AND METHODS: In a retrospective study, patients treated with IVT following stroke were registered. Outcomes were poor outcome (mRS>2), sICH/ECASS-2, and in-hospital mortality. We compared the patients≥80 years who received IVT within 3 hours with those receiving IVT within 3-4.5 hours. We further compared the patients who were <80 years with those ≥80 years and SOTT of 3-4.5 hours. RESULTS: Of 834 patients, 265 aged over 80. In those above 80 and in multivariable analysis, the associations of SOTT with poor outcome (aOR: 1.401, CI: 0.503-3.903, p=0.519), sICH (aOR=2.50, CI=0.76-8.26, p= 0.132) and mortality (aOR=1.12, CI=0.39-3.25, p= 0.833) were not significant. 106 patients received IVT within 3-4.5 hours. In multivariable analysis, the associations of age (≥80 versus <80) with poor outcome (aOR=1.87, CI=0.65-5.37, p=0.246), sICH (aOR=0.65, CI=0.14-3.11, p=0.590), and mortality (aOR=0.87, 95% CI=0.16-4.57, p=0.867) were not significant in patients with SOTT of 3-4.5 hours. CONCLUSION: IVT within 3-4.5 hours in patients ≥80 years is not associated with increased sICH, poor outcome, and mortality compared to the early time window, and also compared to the younger patients in 3-4.5 hours window period. The decision of IVT administration in this age group should not be made solely on the basis of stroke onset timing.

Unraveling the stereochemical and dynamic aspects of the catalytic site of bacterial peptidyl-tRNA hydrolase.

Bacterial peptidyl-tRNA hydrolase (Pth; EC 3.1.1.29) hydrolyzes the peptidyl-tRNAs accumulated in the cytoplasm and thereby prevents cell death by alleviating tRNA starvation. X-ray and NMR studies of Vibrio cholerae Pth (VcPth) and mutants of its key residues involved in catalysis show that the activity and selectivity of the protein depends on the stereochemistry and dynamics of residues H24, D97, N118, and N14. D97-H24 interaction is critical for activity because it increases the nucleophilicity of H24. The N118 and N14 have orthogonally competing interactions with H24, both of which reduce the nucleophilicity of H24 and are likely to be offset by positioning of a peptidyl-tRNA substrate. The region proximal to H24 and the lid region exhibit slow motions that may assist in accommodating the substrate. Helix α3 exhibits a slow wobble with intermediate time scale motions of its N-cap residue N118, which may work as a flypaper to position the scissile ester bond of the substrate. Overall, the dynamics of interactions between the side chains of N14, H24, D97, and N118, control the catalysis of substrate by this enzyme.

Excited-State Trions in Monolayer WS_{2}.

We discover an excited bound three-particle state, the 2s trion, appearing energetically below the 2s exciton in monolayer WS_{2}, using absorption spectroscopy and ab initio GW and Bethe-Salpeter equation calculations. The measured binding energy of the 2s trion (22 meV) is smaller compared to the 1s intravalley and intervalley trions (37 and 31 meV). With increasing temperature, the 1s and 2s trions transfer their oscillator strengths to the respective neutral excitons, establishing an optical fingerprint of trion-exciton resonance pairs. Our discovery underlines the importance of trions for the entire excitation spectrum of two-dimensional semiconductors.

Structural and functional characterization of the transcriptional regulator Rv3488 of Mycobacterium tuberculosis H37Rv.

Rv3488 of Mycobacterium tuberculosis H37Rv has been assigned to the phenolic acid decarboxylase repressor (PadR) family of transcriptional regulators that play key roles in multidrug resistance and virulence of prokaryotes. The binding of cadmium, zinc, and several other metals to Rv3488 was discovered and characterized by isothermal titration calorimetery to be an exothermic process. Crystal structures of apo-Rv3488 and Rv3488 in complex with cadmium or zinc ions were determined by X-ray crystallography. The structure of Rv3488 revealed a dimeric protein with N-terminal winged-helix-turn-helix DNA-binding domains composed of helices α1, α2, α3, and strands ß1 and ß2, with the dimerization interface being formed of helices α4 and α1. The overall fold of Rv3488 was similar to PadR-s2 and metal sensor transcriptional regulators. In the crystal structure of Rv3488-Cd complex, two octahedrally coordinated Cd2+ ions were present, one for each subunit. The same sites were occupied by zinc ions in the structure of Rv3488-Zn, with two additional zinc ions complexed in one monomer. EMSA studies showed specific binding of Rv3488 with its own 30-bp promoter DNA. The functional role of Rv3488 was characterized by expressing the rv3488 gene under the control of hsp60 promoter in Mycobacterium smegmatis Expression of Rv3488 increased the intracellular survival of recombinant M. smegmatis in murine macrophage cell line J774A.1 and also augmented its tolerance to Cd2+ ions. Overall, the studies show that Rv3488 may have transcription regulation and metal-detoxifying functions and its expression in M. smegmatis increases intracellular survival, perhaps by counteracting toxic metal stress.

Structural and Biophysical Characterization of Rab5a from Leishmania Donovani.

Leishmania donovani possess two isoforms of Rab5 (Rab5a and Rab5b), which are involved in fluid phase and receptor-mediated endocytosis, respectively. We have characterized the solution structure and dynamics of a stabilized truncated LdRab5a mutant. For the purpose of NMR structure determination, protein stability was enhanced by systematically introducing various deletions and mutations. Deletion of hypervariable C-terminal and the 20 residues LdRab5a specific insert slightly enhanced the stability, which was further improved by C107S mutation. The final construct, truncated LdRab5a with C107S mutation, was found to be stable for longer durations at higher concentration, with an increase in melting temperature by 10°C. Solution structure of truncated LdRab5a shows the characteristic GTPase fold having nucleotide and effector binding sites. Orientation of switch I and switch II regions match well with that of guanosine 5'-(ß, γ-imido)triphosphate (GppNHp)-bound human Rab5a, indicating that the truncated LdRab5a attains the canonical GTP bound state. However, the backbone dynamics of the P-loop, switch I, and switch II regions were slower than that observed for guanosine 5'-(ß, γ-imido)triphosphate (GMPPNP)-bound H-Ras. This dynamic profile may further complement the residue-specific complementarity in determining the specificity of interaction with the effectors. In parallel, biophysical investigations revealed the urea induced unfolding of truncated LdRab5a to be a four-state process that involved two intermediates, I1 and I2. The maximal 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid (Bis-ANS) binding was observed for I2 state, which was inferred to have molten globule like characteristics. Overall, the strategy presented would have significant impact for studying other Rab and small GTPase proteins by NMR spectroscopy.

Solution structure and dynamics of glia maturation factor from Caenorhabditis elegans.

BACKGROUND: The GMF class of the ADF-H domain family proteins regulate actin dynamics by binding to the Arp2/3 complex and F-actin through their Site-1 and Site-2, respectively. CeGMF of C. elegans is analogous to GMFγ of human and mouse and is 138 amino acids in length. METHODS: We have characterized the solution structure and dynamics of CeGMF by solution NMR spectroscopy and its thermal stability by DSC. RESULTS: The solution structure of CeGMF shows canonical ADF-H fold with two additional ß-strands in the ß4-ß5 loop region. The Site-1 of CeGMF is well formed and residues of all three regions of Site-1 show dynamic flexibility. However, the ß4-ß5 loop of Site-2 is less inclined towards the C-terminal, as the latter is truncated by four residues in comparison to GMF isoforms of human and mouse. Regions of Site-2 show motions on ns-ps timescale, but dynamic flexibility of ß4-ß5 loop is low in comparison to corresponding F-loop region of ADF/cofilin UNC-60B. A general difference in packing of α3 and α1 between GMF and ADF/cofilins was noticed. Additionally, thermal stability of CeGMF was significantly higher than its ADF/cofilin homologs. CONCLUSION: We have presented the first solution structure of GMF from C. elegans, which highlights the structural differences between the Site-2 of CeGMF and mammalian GMF isoforms. Further, we have seen the differences in structure, dynamics, and thermal stability of GMF and ADF/cofilin. GENERAL SIGNIFICANCE: This study provides a useful insight to structural and dynamics factors that define the specificity of GMF towards Arp2/3 complex.

Role of methionine 71 in substrate recognition and structural integrity of bacterial peptidyl-tRNA hydrolase.

BACKGROUND: Bacterial peptidyl-tRNA hydrolase (Pth) is an essential enzyme that alleviates tRNA starvation by recycling prematurely dissociated peptidyl-tRNAs. The specificity of Pth for N-blocked-aminoacyl-tRNA has been proposed to be contingent upon conserved residue N14 forming a hydrogen bond with the carbonyl of the first peptide bond in the substrate. M71 is involved in forming a conserved hydrogen bond with N14. Other interactions facilitating this recognition are not known. METHODS: The structure, dynamics, and stability of the M71A mutant of Pth from Vibrio cholerae (VcPth) were characterized by X-ray crystallography, NMR spectroscopy, MD simulations and DSC. RESULTS: Crystal structure of M71A mutant was determined. In the structure, the dimer interface is formed by the insertion of six C-terminal residues of one molecule into the active site of another molecule. The side-chain amide of N14 was hydrogen bonded to the carbonyl of the last peptide bond formed between residues A196 and E197, and also to A71. The CSP profile of mutation was similar to that observed for the N14D mutant. M71A mutation lowered the thermal stability of the protein. CONCLUSION: Our results indicate that the interactions of M71 with N14 and H24 play an important role in optimal positioning of their side-chains relative to the peptidyl-tRNA substrate. Overall, these interactions of M71 are important for the activity, stability, and compactness of the protein. SIGNIFICANCE: The work presented provides original and new structural and dynamics information that significantly enhances our understanding of the network of interactions that govern this enzyme's activity and selectivity.

Structure, dynamics, and biochemical characterization of ADF/cofilin Twinstar from Drosophilamelanogaster.

BACKGROUND: Twinstar is an ADF/cofilin family protein, which is expressed by the tsr gene in Drosophila melanogaster. Twinstar is one of the main regulators of actin cytoskeleton remodelling and is essential for vital cellular processes like cytokinesis and endocytosis. METHODS: We have characterized the structure and dynamics of Twinstar by solution NMR spectroscopy, the interaction of Twinstar with rabbit muscle actin by ITC, and biochemical activities of Twinstar through different biochemical assays using fluorescence spectroscopy and ultra-centrifugation. RESULTS: The solution structure of Twinstar shows characteristic ADF-H fold with well-formed G/F-site and F-site for interaction with actin. The structure possesses an extended F-loop, which is rigid at the base, but flexible towards its apical region. Twinstar shares similar dynamics for the G/F-site with C. elegans homologs, UNC-60A and UNC-60B. However, the dynamics of its F-loop are different from its C. elegans homologs. Twinstar shows strong affinity for ADP-G-Actin and ATP-G-Actin with Kds of ~7.6 nM and ~0.4 µM, respectively. It shows mild F-actin depolymerizing activity and stable interaction with F-actin with a Kd of ~5.0 µM. It inhibits the rate of the nucleotide exchange in a dose dependent manner. CONCLUSION: On the basis of structure, dynamics, and biochemical activity, Twinstar can be taken to execute its biochemical role by facilitating directional growth and maintenance of length of actin filaments. GENERAL SIGNIFICANCE: This study characterizes the structure, backbone dynamics, and biochemical activities of Twinstar of Drosophila, which provides an insight into the regulation of actin dynamics in the member of phylum insecta.

NMR elucidation of monomer-dimer transition and conformational heterogeneity in histone-like DNA binding protein of Helicobacter pylori.

Helicobacter pylori (H. pylori) colonizes under harsh acidic/oxidative stress conditions of human gastrointestinal tract and can survive there for infinitely longer durations of host life. The bacterium expresses several harbinger proteins to facilitate its persistent colonization under such conditions. One such protein in H. pylori is histone-like DNA binding protein (Hup), which in its homo-dimeric form binds to DNA to perform various DNA dependent cellular activities. Further, it also plays an important role in protecting the genomic DNA from oxidative stress and acidic denaturation. Legitimately, if the binding of Hup to DNA is suppressed, it will directly impact on the survival of the bacterium, thus making Hup a potential therapeutic target for developing new anti-H. pylori agents. However, to inhibit the binding of Hup to DNA, it is necessary to gain detailed insights into the molecular and structural basis of Hup-dimerization and its binding mechanism to DNA. As a first step in this direction, we report here the nuclear magnetic resonance (NMR) assignments and structural features of Hup at pH 6.0. The study revealed the occurrence of dynamic equilibrium between its monomer and dimer conformations. The dynamic equilibrium was found to shifting towards dimer both at low temperature and low pH; whereas DNA binding studies evidenced that the protein binds to DNA in its dimeric form. These preliminary investigations correlate very well with the diverse functionality of protein and will form the basis for future studies aiming to develop novel anti-H. pylori agents employing structure-based-rational drug discovery approach.

Highly Anisotropic in-Plane Excitons in Atomically Thin and Bulklike 1T'-ReSe2.

Atomically thin materials such as graphene or MoS2 are of high in-plane symmetry. Crystals with reduced symmetry hold the promise for novel optoelectronic devices based on their anisotropy in current flow or light polarization. Here, we present polarization-resolved optical transmission and photoluminescence spectroscopy of excitons in 1T'-ReSe2. On reducing the crystal thickness from bulk to a monolayer, we observe a strong blue shift of the optical band gap from 1.37 to 1.50 eV. The excitons are strongly polarized with dipole vectors along different crystal directions, which persist from bulk down to monolayer thickness. The experimental results are well reproduced by ab initio calculations based on the GW-BSE approach within LDA+GdW approximation. The excitons have high binding energies of 860 meV for the monolayer and 120 meV for bulk. They are strongly confined within a single layer even for the bulk crystal. In addition, we find in our calculations a direct band gap in 1T'-ReSe2 regardless of crystal thickness, indicating weak interlayer coupling effects on the band gap characteristics. Our results pave the way for polarization-sensitive applications, such as optical logic circuits operating in the infrared spectral region.

Molecular characterization of novel immunodominant molybdenum cofactor biosynthesis protein C1 (Rv3111) from Mycobacterium tuberculosis H37Rv.

BACKGROUND: In the molybdenum cofactor biosynthesis pathway, MoaA and MoaC catalyze the first step of transformation of GTP to cPMP. In M. tuberculosis H37Rv, three different genes (Rv3111, Rv0864 and Rv3324c) encode for MoaC homologs. Out of these three only MoaC1 (Rv3111) is secretory in nature. METHODS: We have characterized MoaC1 protein through biophysical, in-silico, and immunological techniques. RESULTS: We have characterized the conformation and thermodynamic stability of MoaC1, and have established its secretory nature by demonstrating the presence of anti-MoaC1 antibodies in human tuberculosis patients' sera. Further, MoaC1 elicited a dominant Th1 immune response in mice characterized by increased induction of IL-2 and IFN-γ. CONCLUSION: Integrating these results, we conclude that MoaC1 is a structured secretory protein capable of binding with GTP and eliciting induced immune response. GENERAL SIGNIFICANCE: This study would be useful for the development of vaccines against tuberculosis and to improve methods used for diagnosis of tuberculosis.

Structural characterization of peptidyl-tRNA hydrolase from Mycobacterium smegmatis by NMR spectroscopy.

BACKGROUND: Accumulation of toxic peptidyl-tRNAs in the bacterial cytoplasm is averted by the action of peptidyl-tRNA hydrolase (Pth), which cleaves peptidyl-tRNA into free tRNA and peptide. NMR studies are needed for a protein homolog with a complete crystal structure, for comparison with the NMR structure of Mycobacterium tuberculosis Pth. METHODS: The structure and dynamics of Mycobacterium smegmatis Pth (MsPth) were characterized by NMR spectroscopy and MD simulations. The thermal stability of MsPth was characterized by DSC. RESULTS: MsPth NMR structure has a central mixed seven stranded ß-sheet that is enclosed by six α-helices. NMR relaxation and MD simulations studies show that most of the ordered regions are rigid. Of the substrate binding segments, the gate loop is rigid, the base loop displays slow motions, while the lid loop displays fast timescale motions. MsPth displays high thermal stability characterized by a melting temperature of 61.71°C. CONCLUSION: The NMR structure of MsPth shares the canonical Pth fold with the NMR structure of MtPth. The motional characteristics for the lid region, the tip of helix α3, and the gate region, as indicated by MD simulations and NMR data, are similar for MsPth and MtPth. However, MsPth has relatively less rigid base loop and more compactly packed helices α5 and α6. The packing and the dynamic differences appear to be an important contributing factor to the thermal stability of MsPth, which is significantly higher than that of MtPth. SIGNIFICANCE: MsPth structure consolidates our understanding of the structure and dynamics of bacterial Pth proteins.

Phonon Sidebands in Monolayer Transition Metal Dichalcogenides.

Excitons dominate the optical properties of monolayer transition metal dichalcogenides (TMDs). Besides optically accessible bright exciton states, TMDs exhibit also a multitude of optically forbidden dark excitons. Here, we show that efficient exciton-phonon scattering couples bright and dark states and gives rise to an asymmetric excitonic line shape. The observed asymmetry can be traced back to phonon-induced sidebands that are accompanied by a polaron redshift. We present a joint theory-experiment study investigating the microscopic origin of these sidebands in different TMD materials taking into account intra- and intervalley scattering channels opened by optical and acoustic phonons. The gained insights contribute to a better understanding of the optical fingerprint of these technologically promising nanomaterials.