Tail length and E525K dilated cardiomyopathy mutant alter human β-cardiac myosin super-relaxed state

Dilated cardiomyopathy (DCM) is a condition characterized by impaired cardiac function, due to myocardial hypo-contractility, and is associated with point mutations in β-cardiac myosin, the molecular motor that powers cardiac contraction. Myocardial function can be modulated through sequestration of myosin motors into an auto-inhibited "super-relaxed" state (SRX), which may be further stabilized by a structural state known as the "interacting heads motif" (IHM). Here, we sought to determine whether hypo-contractility of DCM myocardium results from reduced function of individual myosin molecules or from decreased myosin availability to interact with actin due to increased IHM/SRX stabilization. We used an established DCM myosin mutation, E525K, and characterized the biochemical and mechanical activity of wild-type and mutant human β-cardiac myosin constructs that differed in the length of their coiled-coil tail, which dictates their ability to form the IHM/SRX state. We found that short-tailed myosin constructs exhibited low IHM/SRX content, elevated actin-activated ATPase activity, and fast velocities in unloaded motility assays. Conversely, longer-tailed constructs exhibited higher IHM/SRX content and reduced actomyosin ATPase and velocity. Our modeling suggests that reduced velocities may be attributed to IHM/SRX-dependent sequestration of myosin heads. Interestingly, longer-tailed E525K mutants showed no apparent impact on velocity or actomyosin ATPase at low ionic strength but stabilized IHM/SRX state at higher ionic strength. Therefore, the hypo-contractility observed in DCM may be attributable to reduced myosin head availability caused by enhanced IHM/SRX stability in E525K mutants.

Tail Length and E525K Dilated Cardiomyopathy Mutant Alter Human β-Cardiac Myosin Super-Relaxed State

Dilated cardiomyopathy (DCM) is characterized by impaired cardiac function due to myocardial hypo-contractility and is associated with point mutations in β-cardiac myosin, the molecular motor that powers cardiac contraction. Myocardial function can be modulated through sequestration of myosin motors into an auto-inhibited "super relaxed" state (SRX), which is further stabilized by a structural state known as the "Interacting Heads Motif" (IHM). Therefore, hypo-contractility of DCM myocardium may result from: 1) reduced function of individual myosin, and/or; 2) decreased myosin availability due to increased IHM/SRX stabilization. To define the molecular impact of an established DCM myosin mutation, E525K, we characterized the biochemical and mechanical activity of wild-type (WT) and E525K human β-cardiac myosin constructs that differed in the length of their coiled-coil tail, which dictates their ability to form the IHM/SRX state. Single-headed (S1) and a short-tailed, double-headed (2HEP) myosin constructs exhibited low (~10%) IHM/SRX content, actin-activated ATPase activity of ~5s-1 and fast velocities in unloaded motility assays (~2000nm/s). Double-headed, longer-tailed (15HEP, 25HEP) constructs exhibited higher IHM/SRX content (~90%), and reduced actomyosin ATPase (<1s-1) and velocity (~800nm/s). A simple analytical model suggests that reduced velocities may be attributed to IHM/SRXdependent sequestration of myosin heads. Interestingly, the E525K 15HEP and 25HEP mutants showed no apparent impact on velocity or actomyosin ATPase at low ionic strength. However, at higher ionic strength, the E525K mutation stabilized the IHM/SRX state. Therefore, the E525K-associated DCM human cardiac hypo-contractility may be attributable to reduced myosin head availability caused by enhanced IHM/SRX stability.

Cellular Lipids Regulate the Conformational Ensembles of the Disordered Intracellular Loop 3 in β2 Adrenergic Receptor

The structurally disordered intracellular loops (ICLs) of G protein-coupled receptors (GPCRs) play a critical role in G protein coupling. In our previous work, we used a combination of FRET-based and computational methodologies to show that the third intracellular loop (ICL3) modulates the activity and G protein coupling selectivity in GPCRs. In the current study, we have uncovered the role of several lipid components in modulating the conformational ensemble of ICL3 of the β2-adrenergic receptor (β2AR). Our findings indicate that phosphatidylinositol 4,5-bisphosphate (PIP2) in the inner leaflet of the membrane bilayer acts as a stabilizing anchor for ICL3, opening the intracellular cavity to facilitate G protein coupling. This interaction between PIP2 and ICL3 causes tilting of β2AR within the cellular membrane. Notably, this tilting of the receptor is supported by ganglioside GM3 stabilizing the extracellular loops on the outer leaflet of the bilayer, thereby exerting an allosteric effect on the orthosteric ligand binding pocket. Our results underscore the significance of lipids in modulating GPCR activity, proposing an allosteric mechanism that occurs through the receptor's orientation within the membrane.

Autoregulation of GPCR signalling through the third intracellular loop

The third intracellular loop (ICL3) of the G protein-coupled receptor (GPCR) fold is important for the signal transduction process downstream of receptor activation1-3. Despite this, the lack of a defined structure of ICL3, combined with its high sequence divergence among GPCRs, complicates characterization of its involvement in receptor signalling4. Previous studies focusing on the β2 adrenergic receptor (β2AR) suggest that ICL3 is involved in the structural process of receptor activation and signalling5-7. Here we derive mechanistic insights into the role of ICL3 in β2AR signalling, observing that ICL3 autoregulates receptor activity through a dynamic conformational equilibrium between states that block or expose the receptor's G protein-binding site. We demonstrate the importance of this equilibrium for receptor pharmacology, showing that G protein-mimetic effectors bias the exposed states of ICL3 to allosterically activate the receptor. Our findings additionally reveal that ICL3 tunes signalling specificity by inhibiting receptor coupling to G protein subtypes that weakly couple to the receptor. Despite the sequence diversity of ICL3, we demonstrate that this negative G protein-selection mechanism through ICL3 extends to GPCRs across the superfamily, expanding the range of known mechanisms by which receptors mediate G protein subtype selective signalling. Furthermore, our collective findings suggest ICL3 as an allosteric site for receptor- and signalling pathway-specific ligands.

Dilated cardiomyopathy mutation E525K in human beta-cardiac myosin stabilizes the interacting-heads motif and super-relaxed state of myosin

The auto-inhibited, super-relaxed (SRX) state of cardiac myosin is thought to be crucial for regulating contraction, relaxation, and energy conservation in the heart. We used single ATP turnover experiments to demonstrate that a dilated cardiomyopathy (DCM) mutation (E525K) in human beta-cardiac myosin increases the fraction of myosin heads in the SRX state (with slow ATP turnover), especially in physiological ionic strength conditions. We also utilized FRET between a C-terminal GFP tag on the myosin tail and Cy3ATP bound to the active site of the motor domain to estimate the fraction of heads in the closed, interacting-heads motif (IHM); we found a strong correlation between the IHM and SRX state. Negative stain electron microscopy and 2D class averaging of the construct demonstrated that the E525K mutation increased the fraction of molecules adopting the IHM. Overall, our results demonstrate that the E525K DCM mutation may reduce muscle force and power by stabilizing the auto-inhibited SRX state. Our studies also provide direct evidence for a correlation between the SRX biochemical state and the IHM structural state in cardiac muscle myosin. Furthermore, the E525 residue may be implicated in crucial electrostatic interactions that modulate this conserved, auto-inhibited conformation of myosin.

Kinesin-3 motors are fine-tuned at the molecular level to endow distinct mechanical outputs

BACKGROUND

Kinesin-3 family motors drive diverse cellular processes and have significant clinical importance. The ATPase cycle is integral to the processive motility of kinesin motors to drive long-distance intracellular transport. Our previous work has demonstrated that kinesin-3 motors are fast and superprocessive with high microtubule affinity. However, chemomechanics of these motors remain poorly understood.

RESULTS

We purified kinesin-3 motors using the Sf9-baculovirus expression system and demonstrated that their motility properties are on par with the motors expressed in mammalian cells. Using biochemical analysis, we show for the first time that kinesin-3 motors exhibited high ATP turnover rates, which is 1.3- to threefold higher compared to the well-studied kinesin-1 motor. Remarkably, these ATPase rates correlate to their stepping rate, suggesting a tight coupling between chemical and mechanical cycles. Intriguingly, kinesin-3 velocities (KIF1A > KIF13A > KIF13B > KIF16B) show an inverse correlation with their microtubule-binding affinities (KIF1A < KIF13A < KIF13B < KIF16B). We demonstrate that this differential microtubule-binding affinity is largely contributed by the positively charged residues in loop8 of the kinesin-3 motor domain. Furthermore, microtubule gliding and cellular expression studies displayed significant microtubule bending that is influenced by the positively charged insert in the motor domain, K-loop, a hallmark of kinesin-3 family.

CONCLUSIONS

Together, we propose that a fine balance between the rate of ATP hydrolysis and microtubule affinity endows kinesin-3 motors with distinct mechanical outputs. The K-loop, a positively charged insert in the loop12 of the kinesin-3 motor domain promotes microtubule bending, an interesting phenomenon often observed in cells, which requires further investigation to understand its cellular and physiological significance.

Effect of Ligands and Transducers on the Neurotensin Receptor 1 Conformational Ensemble

Using a discrete, intracellular ¹⁹F nuclear magnetic resonance (NMR) probe on transmembrane helix 6 of the neurotensin receptor 1 (NTS1), we aim to understand how ligands and transducers modulate the receptor's structural ensemble in a solution. For apo NTS1, ¹⁹F NMR spectra reveal an ensemble of at least three conformational substates (one inactive and two active-like) in equilibrium that exchange on the millisecond to second timescale. Dynamic NMR experiments reveal that these substates follow a linear three-site exchange process that is both thermodynamically and kinetically remodeled by orthosteric ligands. As previously observed in other G protein-coupled receptors (GPCRs), the full agonist is insufficient to completely stabilize the active-like state. The inactive substate is abolished upon coupling to β-arrestin-1 (βArr1) or the C-terminal helix of Gα_q, which comprises ≳60% of the GPCR/G protein interface surface area. Whereas βArr1 exclusively selects for pre-existing active-like substates, the Gα_q peptide induces a new substate. Both transducer molecules promote substantial line broadening of active-like states, suggesting contributions from additional microsecond to millisecond exchange processes. Together, our study suggests that (i) the NTS1 allosteric activation mechanism may be alternatively dominated by induced fit or conformational selection depending on the coupled transducer, and (ii) the available static structures do not represent the entire conformational ensemble observed in a solution.

Nanosurfer Assay Dissects β-Cardiac Myosin and Cardiac Myosin-Binding Protein C Interactions

Cardiac myosin-binding protein C (cMyBP-C) modulates cardiac contractility through putative interactions with the myosin S2 tail and/or the thin filament. The relative contribution of these binding-partner interactions to cMyBP-C modulatory function remains unclear. Hence, we developed a "nanosurfer" assay as a model system to interrogate these cMyBP-C binding-partner interactions. Synthetic thick filaments were generated using recombinant human β-cardiac myosin subfragments (HMM or S1) attached to DNA nanotubes, with 14 or 28 nm spacing, corresponding to the 14.3 nm myosin spacing in native thick filaments. The nanosurfer assay consists of DNA nanotubes added to the in vitro motility assay so that myosins on the motility surface effectively deliver thin filaments to the DNA nanotubes, enhancing thin filament gliding probability on the DNA nanotubes. Thin filament velocities on nanotubes with either 14 or 28 nm myosin spacing were no different. We then characterized the effects of cMyBP-C on thin filament motility by alternating HMM and cMyBP-C N-terminal fragments (C0-C2 or C1-C2) on nanotubes every 14 nm. Both C0-C2 and C1-C2 reduced thin filament velocity 4-6 fold relative to HMM alone. Similar inhibition occurred using the myosin S1 construct, which lacks the myosin S2 region proposed to interact with cMyBP-C, suggesting that the cMyBP-C N-terminus must interact with other myosin head domains and/or actin to slow thin filament velocity. Thin filament velocity was unaffected by the C0-C1f fragment, which lacks the majority of the M-domain, supporting the importance of this domain for inhibitory interaction(s). A C0-C2 fragment with phosphomimetic replacement in the M-domain showed markedly less inhibition of thin filament velocity compared to its phosphonull counterpart, highlighting the modulatory role of M-domain phosphorylation on cMyBP-C function. Therefore, the nanosurfer assay provides a platform to precisely manipulate spatially dependent cMyBP-C binding partner interactions, shedding light on the molecular regulation of β-cardiac myosin contractility.

Multimodal regulation of myosin VI ensemble transport by cargo adaptor protein GIPC

A range of cargo adaptor proteins are known to recruit cytoskeletal motors to distinct subcellular compartments. However, the structural impact of cargo recruitment on motor function is poorly understood. Here, we dissect the multimodal regulation of myosin VI activity through the cargo adaptor GAIP-interacting protein, C terminus (GIPC), whose overexpression with this motor in cancer enhances cell migration. Using a range of biophysical techniques, including motility assays, FRET-based conformational sensors, optical trapping, and DNA origami-based cargo scaffolds to probe the individual and ensemble properties of GIPC-myosin VI motility, we report that the GIPC myosin-interacting region (MIR) releases an autoinhibitory interaction within myosin VI. We show that the resulting conformational changes in the myosin lever arm, including the proximal tail domain, increase the flexibility of the adaptor-motor linkage, and that increased flexibility correlates with faster actomyosin association and dissociation rates. Taken together, the GIPC MIR-myosin VI interaction stimulates a twofold to threefold increase in ensemble cargo speed. Furthermore, the GIPC MIR-myosin VI ensembles yield similar cargo run lengths as forced processive myosin VI dimers. We conclude that the emergent behavior from these individual aspects of myosin regulation is the fast, processive, and smooth cargo transport on cellular actin networks. Our study delineates the multimodal regulation of myosin VI by the cargo adaptor GIPC, while highlighting linkage flexibility as a novel biophysical mechanism for modulating cellular cargo motility.

Rowell Syndrome: A True Entity or a Diagnostic Challenge?

Lupus Erythematosus (LE) is an inflammatory condition of the connective tissue which manifests in variable forms. Rowell syndrome is a rare entity, with a female preponderance, where there is the presence of both LE and Erythema Multiforme (EM)-like lesions. Such patients are positive for antinuclear, anti-Ro/La and rheumatoid factor. Subcutaneous LE (SCLE) and EM can often share characteristics. The presence of lesions resembling both the conditions can pose a diagnostic difficulty, especially in the absence of complete clarity on the existence of Rowell syndrome. Present case is of a 47-year-old female, who presented with rashes over the face and trunk, along with photosensitivity. Cutaneous examination revealed multiple erythematous hyperpigmented plaques over the face with atypical targetoid lesions over the trunk and limbs. The diagnosis of Rowell’s syndrome was confirmed based on immunology and histopathology. This case has been reported to highlight the importance of delving into the various presentations of LE.

Squamous Cell Carcinoma Complicating Plaque of Lupus Erythematosus - A Case Series

Lupus Erythematosus is a multisystem disorder with a wide spectrum of clinical presentations ranging from cutaneous involvement to widespread systemic involvement. Squamous cell carcinoma formation in cutaneous lesions of LE is rare but had greater chances of metastases. Here, we report two cases, one of Discoid Lupus Erythematosus and other of Systemic Lupus Erythematosus complicated by development of squamous cell carcinoma over cutaneous lesions.

KIF13A motors are regulated by Rab22A to function as weak dimers inside the cell

Endocytic recycling is a complex itinerary, critical for many cellular processes. Membrane tubulation is a hallmark of recycling endosomes (REs), mediated by KIF13A, a kinesin-3 family motor. Understanding the regulatory mechanism of KIF13A in RE tubulation and cargo recycling is of fundamental importance but is overlooked. Here, we report a unique mechanism of KIF13A dimerization modulated by Rab22A, a small guanosine triphosphatase, during RE tubulation. A conserved proline between neck coil-coiled-coil (NC-CC1) domains of KIF13A creates steric hindrance, rendering the motors as inactive monomers. Rab22A plays an unusual role by binding to NC-CC1 domains of KIF13A, relieving proline-mediated inhibition and facilitating motor dimerization. As a result, KIF13A motors produce balanced motility and force against multiple dyneins in a molecular tug-of-war to regulate RE tubulation and homeostasis. Together, our findings demonstrate that KIF13A motors are tuned at a single-molecule level to function as weak dimers on the cellular cargo.

Kinase inhibitors allosterically disrupt a regulatory interaction to enhance PKCα membrane translocation

The eukaryotic kinase domain has multiple intrinsically disordered regions whose conformation dictates kinase activity. Small molecule kinase inhibitors (SMKIs) rely on disrupting the active conformations of these disordered regions to inactivate the kinase. While SMKIs are selected for their ability to cause this disruption, the allosteric effects of conformational changes in disordered regions is limited by a lack of dynamic information provided by traditional structural techniques. In this study, we integrated multiscale molecular dynamics simulations with FRET sensors to characterize a novel allosteric mechanism that is selectively triggered by SMKI binding to the protein kinase Cα domain. The indole maleimide inhibitors BimI and sotrastaurin were found to displace the Gly-rich loop (G-loop) that normally shields the ATP-binding site. Displacement of the G-loop interferes with a newly identified, structurally conserved binding pocket for the C1a domain on the N lobe of the kinase domain. This binding pocket, in conjunction with the N-terminal regulatory sequence, masks a diacylglycerol (DAG) binding site on the C1a domain. SMKI-mediated displacement of the G-loop released C1a and exposed the DAG binding site, enhancing protein kinase Cα translocation both to synthetic lipid bilayers and to live cell membranes in the presence of DAG. Inhibitor chemotype determined the extent of the observed allosteric effects on the kinase domain and correlated with the extent of membrane recruitment. Our findings demonstrate the allosteric effects of SMKIs beyond the confines of kinase catalytic conformation and provide an integrated computational-experimental paradigm to investigate parallel mechanisms in other kinases.

Dynamic multimerization of Dab2-Myosin VI complexes regulates cargo processivity while minimizing cortical actin reorganization

Myosin VI ensembles on endocytic cargo facilitate directed transport through a dense cortical actin network. Myosin VI is recruited to clathrin-coated endosomes via the cargo adaptor Dab2. Canonically, it has been assumed that the interactions between a motor and its cargo adaptor are stable. However, it has been demonstrated that the force generated by multiple stably attached motors disrupts local cytoskeletal architecture, potentially compromising transport. In this study, we demonstrate that dynamic multimerization of myosin VI-Dab2 complexes facilitates cargo processivity without significant reorganization of cortical actin networks. Specifically, we find that Dab2 myosin interacting region (MIR) binds myosin VI with a moderate affinity (184 nM) and single-molecule kinetic measurements demonstrate a high rate of turnover (1 s⁻¹) of the Dab2 MIR–myosin VI interaction. Single-molecule motility shows that saturating Dab2-MIR concentration (2 μM) promotes myosin VI homodimerization and processivity with run lengths comparable with constitutive myosin VI dimers. Cargo-mimetic DNA origami scaffolds patterned with Dab2 MIR-myosin VI complexes are weakly processive, displaying sparse motility on single actin filaments and “stop-and-go” motion on a cellular actin network. On a minimal actin cortex assembled on lipid bilayers, unregulated processive movement by either constitutive myosin V or VI dimers results in actin remodeling and foci formation. In contrast, Dab2 MIR–myosin VI interactions preserve the integrity of a minimal cortical actin network. Taken together, our study demonstrates the importance of dynamic motor–cargo association in enabling cargo transportation without disrupting cytoskeletal organization.

Allosteric modulation of adenosine A1 and cannabinoid 1 receptor signaling by G-peptides

While allosteric modulation of GPCR signaling has gained prominence to address the need for receptor specificity, efforts have mainly focused on allosteric sites adjacent to the orthosteric ligand-binding pocket and lipophilic molecules that target transmembrane helices. In this study, we examined the allosteric influence of native peptides derived from the C-terminus of the Gα subunit (G-peptides) on signaling from two Gi-coupled receptors, adenosine A1 receptor (A1 R) and cannabinoid receptor 1 (CB1 ). We expressed A1 R and CB1 fusions with G-peptides derived from Gαs, Gαi, and Gαq in HEK 293 cells using systematic protein affinity strength modulation (SPASM) and monitored the impact on downstream signaling in the cell compared to a construct lacking G-peptides. We used agonists N6 -Cyclopentyladenosine (CPA) and 5'-N-Ethylcarboxamidoadenosine (NECA) for A1 R and 2-Arachidonoylglycerol (2-AG) and WIN 55,212-2 mesylate (WN) for CB1 . G-peptides derived from Gαi and Gαq enhance agonist-dependent cAMP inhibition, demonstrating their effect as positive allosteric modulators of Gi-coupled signaling. In contrast, both G-peptides suppress agonist-dependent IP1 levels suggesting that they differentially function as negative allosteric modulators of Gq-coupled signaling. Taken together with our previous studies on Gs-coupled receptors, this study provides an extended model for the allosteric effects of G-peptides on GPCR signaling, and highlights their potential as probe molecules to enhance receptor specificity.

ER/K-link-Leveraging a native protein linker to probe dynamic cellular interactions

ER/K α-helices are a subset of single alpha helical domains, which exhibit unusual stability as isolated protein secondary structures. They adopt an elongated structural conformation, while regulating the frequency of interactions between proteins or polypeptides fused to their ends. Here we review recent advances on the structure, stability and function of ER/K α-helices as linkers (ER/K linkers) in native proteins. We describe methodological considerations in the molecular cloning, protein expression and measurement of interaction strengths, using sensors incorporating ER/K linkers. We highlight biological insights obtained over the last decade by leveraging distinct biophysical features of ER/K-linked sensors. We conclude with the outlook for the use of ER/K linkers in the selective modulation of dynamic cellular interactions.

Optical Mapping of cAMP Signaling at the Nanometer Scale

Cells relay a plethora of extracellular signals to specific cellular responses by using only a few second messengers, such as cAMP. To explain signaling specificity, cAMP-degrading phosphodiesterases (PDEs) have been suggested to confine cAMP to distinct cellular compartments. However, measured rates of fast cAMP diffusion and slow PDE activity render cAMP compartmentalization essentially impossible. Using fluorescence spectroscopy, we show that, contrary to earlier data, cAMP at physiological concentrations is predominantly bound to cAMP binding sites and, thus, immobile. Binding and unbinding results in largely reduced cAMP dynamics, which we term "buffered diffusion." With a large fraction of cAMP being buffered, PDEs can create nanometer-size domains of low cAMP concentrations. Using FRET-cAMP nanorulers, we directly map cAMP gradients at the nanoscale around PDE molecules and the areas of resulting downstream activation of cAMP-dependent protein kinase (PKA). Our study reveals that spatiotemporal cAMP signaling is under precise control of nanometer-size domains shaped by PDEs that gate activation of downstream effectors.

An overview of organic matters in municipal wastewater: Removal via self-assembly flocculating mechanism and the molecular level characterization

On considering the critical issues in attaining stringent water quality standards and not creating any environmental impacts, we focused for the first time the economically feasible, emerging technology known as Self-assembly flocculating (Saf process). In which, the study investigated the applicability of bioflocculant (a biopolymer-self-assembly in nature) act as a surrogates on relying the removal of broad spectrum of substances under optimized conditions (Dosage: 90 mg/L; pH: 7; CaCl₂). On using different techniques, the results have proved in removing the organic matter such as pharmaceuticals (Gentamycin, Cholecalciferol, Fluvoxamine, 3-OH Desogestrel, and Pheniramine), endocrine disturbing compounds [Phthalic acid, Benzene, 1, 2, 4 -Trimethoxy-5-(1-Propenyl)-, Benzene, 1, 2-Dimethoxy-4-(2-Propenyl)-, 1, 2-Benzenedicarboxylic Acid, 3-Cyclohexen-1-ol], fluorescent components (Polysaccharide like material), and others. The toxicological assessment of self-assembly bioflocculant implemented on zebra fish were statistically correlated [r = 0.95, p < 0.01 and 0.05 for P₁WW; r = 0.91, p < 0.01 and 0.05 for P₂WW] and [r = 0.7 5, p < 0.05 for P₁WT; r = 0.095, p < 0.01 and 0.05 for P₂WT]. This integrated approach supplemented further information of zeta potential (-16 mV in P₁WW and -14.6 mV in P₂WW decreased to -1.05 mV and -1.56 mV) with particle size distribution to explain via Saf process. In this research, the new insight has established non-toxic, self-assembly, biodegradable, bioflocculant for effective bioremediation.

Evolving high-throughput approaches to assess the environmental risk of sewage water at molecular level: comprehensive study

Dissolved organic matter (DOM) especially anthropogenic compounds in sewage systems affects their ultimate fate in the environment which is challenging to ascertain the heterogenic nature of the compound and causes co-occurring effects in most aquatic samples. So, our study have focused on current approaches to the chemical and structural characterization of DOM with the detailed classification of individual compounds such as the molecular levels of volatile organic, inorganic materials, drugs and endocrine disrupting compounds. Analytical techniques for example high performance gas chromatography-mass spectrometry (GCMS) with high-resolution liquid chromatography (HR-LCMS), X-ray diffraction (XRD) and three-dimensional fluorescence excitation emission matrix (3D-EEM) has resulted in advancing the parametric studies. In addition, the toxicological assessment of an aquatic organism (zebrafish as a model) has ensued in enlightening the risk of contaminated sources. The result of the research highlighted the efficacy of high-throughput approaches to assess the environmental impact of sewage water.

Characterization of self-assembled bioflocculant from the microbial consortium and its applications

Bioflocculant has been recently exploited in various research activities. In this research, we report for the first time that a novel bioflocculant can self-assemble into nanoparticles with an irregular structure in solution. Bioflocculant has been developed from novel consortium encompassing Enterococcus faecalis, Proteus mirabilis, Lysini bacillus sp., inoculated into the modified medium such as hydrolyzed wheat bran and rice bran extract. Characterization of bioflocculant shows that it is made up of mannose, fructose, raffinose, and galactose with a slightly negative charges. They are further characterized by FTIR and XPS. 3D-EEM and MALDITOF-MS are confirmed the proteoglycan nature of the bioflocculant. These bioflocculant not only exhibits greater biosorption of heavy metals by self-flocculating (or) self-aggregating activity, but also possesses mosquitocidal and anti-biofilm activity due to its cell surface modification. Further research have to be carried out regarding the mechanism of self-assembly nature of bioflocculant into nanoparticle in solution which provide a new path for bioremediation and biomedical application.

Minute-scale persistence of a GPCR conformation state triggered by non-cognate G protein interactions primes signaling

Despite the crowded nature of the cellular milieu, ligand-GPCR-G protein interactions are traditionally viewed as spatially and temporally isolated events. In contrast, recent reports suggest the spatial and temporal coupling of receptor-effector interactions, with the potential to diversify downstream responses. In this study, we combine protein engineering of GPCR-G protein interactions with affinity sequestration and photo-manipulation of the crucial Gα C terminus, to demonstrate the temporal coupling of cognate and non-cognate G protein interactions through priming of the GPCR conformation. We find that interactions of the Gαs and Gαq C termini with the β₂-adrenergic receptor (β₂-AR), targeted at the G-protein-binding site, enhance Gs activation and cyclic AMP levels. β₂-AR-Gα C termini interactions alter receptor conformation, which persists for ~90 s following Gα C terminus dissociation. Non-cognate G-protein expression levels impact cognate signaling in cells. Our study demonstrates temporal allostery in GPCRs, with implications for the modulation of downstream responses through the canonical G-protein-binding interface.

Stiffness of Cargo-Motor Linkage Tunes Myosin VI Motility and Response to Load

We examine the effect of cargo-motor linkage stiffness on the mechanobiological properties of the molecular motor myosin VI. We use the programmability of DNA nanostructures to modulate cargo-motor linkage stiffness and combine it with high-precision optical trapping measurements to measure the effect of linkage stiffness on the motile properties of myosin VI. Our results reveal that a stiff cargo-motor linkage leads to shorter step sizes and load-induced anchoring of myosin VI, while a flexible linkage results in longer steps with frequent detachments from the actin filament under load. Our findings suggest a novel regulatory mechanism for tuning the dual cellular roles of the anchor and transporter ascribed to myosin VI.

Conformational plasticity of the intracellular cavity of GPCR-G-protein complexes leads to G-protein promiscuity and selectivity

While the dynamics of the intracellular surface in agonist-stimulated GPCRs is well studied, the impact of GPCR dynamics on G-protein selectivity remains unclear. Here, we combine molecular dynamics simulations with live-cell FRET and secondary messenger measurements, for 21 GPCR-G-protein combinations, to advance a dynamic model of the GPCR-G-protein interface. Our data show C terminus peptides of Gαs, Gαi, and Gαq proteins assume a small ensemble of unique orientations when coupled to their cognate GPCRs, similar to the variations observed in 3D structures of GPCR-G-protein complexes. The noncognate G proteins interface with latent intracellular GPCR cavities but dissociate due to weak and unstable interactions. Three predicted mutations in β2-adrenergic receptor stabilize binding of noncognate Gαq protein in its latent cavity, allowing promiscuous signaling through both Gαs and Gαq in a dose-dependent manner. This demonstrates that latent GPCR cavities can be evolved, by design or nature, to tune G-protein selectivity, giving insights to pluridimensional GPCR signaling.

Fabrication of MgO nanostructures and its efficient photocatalytic, antibacterial and anticancer performance

Magnesium oxide (MgO) nanostructures were prepared using microwave-assisted (M 1) and hydrothermal (M 2) methods and characterized by XRD, SEM and FT-IR. It exhibits cubic structure with an average crystallite size of 20 nm (M 1) and 14 nm (M 2) and the lattice strain (WH plot) is 0.0017 (M 1), 0.0037 (M 2). It's spherical and rods like structures are confirmed through SEM and TEM. The vibrational stretching mode of MgO is 439 (M 1) and 449 cm^-1 (M 2). The optical bandgap is estimated as 5.93 eV (M 1) and 5.85 eV (M 2) through UV-Vis spectra. The fluorescence spectrum shows emission peaks at 414 and 437 (M 1) and 367 and 385 nm (M 2). The photodegradation studies of MgO nanostructures were assessed by monitoring the decolorization of methylene blue and Congo red dyes in aqueous solution under sunlight irradiation. The antibacterial activities of M 1 and M 2 are investigated against the gram-negative (Escherichia coli, Shigella flexneri, Salmonella typhi, Proteus mirabilis, Aeromonas hydrophila and Vibrio cholera) and gram-positive (Bacillus subtilis and Rhodococcus rhodochrous) bacteria. The zone of inhibition of 24 (M 1) and 25 mm (M 2) indicates high antibacterial activity towards the gram negative bacterium A. hydrophila. Confocal laser scanning microscopic (CLSM) analysis was utilized for understanding the variation in antibacterial activity between different orientations of MgO nanostructures. The cytotoxicity assay confirmed that the prepared nanostructures are non - toxic to normal healthy RBC's. In-vitro anticancer efficiency (IC₅₀) of MgO nanostructures against human lung cancer cell line (A549) was investigated.

Bitopic Inhibition of ATP and Substrate Binding in Ser/Thr Kinases through a Conserved Allosteric Mechanism

Protein kinases achieve substrate selective phosphorylation through their conformational flexibility and dynamic interaction with the substrate. Designing substrate selective or kinase selective small molecule inhibitors remains a challenge because of a lack of understanding of the dynamic mechanism by which substrates are selected by the kinase. Using a combination of all-atom molecular dynamics simulations and FRET sensors, we have delineated an allosteric mechanism that results in interaction among the DFG motif, G-loop, and activation loop and structurally links the nucleotide and substrate binding interfaces in protein kinase Cα and three other Ser/Thr kinases. ATP-competitive staurosporine analogues engage this allosteric switch region located just outside the ATP binding site to displace substrate binding to varying degrees. These inhibitors function as bitopic ligands by occupying the ATP binding site and interacting with the allosteric switch region. The conserved mechanism identified in this study can be exploited to select and design bitopic inhibitors for kinases.

Engaging myosin VI tunes motility, morphology and identity in endocytosis

While unconventional myosins interact with different stages of the endocytic pathway, they are ascribed a transport function that is secondary to the protein complexes that control organelle identity. Endosomes are subject to a dynamic, continuous flux of proteins that control their characteristic properties, including their motility within the cell. Efforts to describe the changes in identity of this compartment have largely focused on the adaptors present on the compartment and not on the motile properties of the compartment itself. In this study, we use a combination of optogenetic and chemical-dimerization strategies to target exogenous myosin VI to early endosomes, and probe its influence on organelle motility, morphology and identity. Our analysis across timescales suggests a model wherein the artificial engagement of myosin VI motility on early endosomes restricts microtubule-based motion, followed by morphological changes characterized by the rapid condensation and disintegration of organelles, ultimately leading to the enhanced overlap of markers that demarcate endosomal compartments. Together, our findings show that synthetic engagement of myosin VI motility is sufficient to alter organelle homeostasis in the endocytic pathway.

Distinct structural mechanisms determine substrate affinity and kinase activity of protein kinase Cα

Protein kinase Cα (PKCα) belongs to the family of AGC kinases that phosphorylate multiple peptide substrates. Although the consensus sequence motif has been identified and used to explain substrate specificity for PKCα, it does not inform the structural basis of substrate-binding and kinase activity for diverse substrates phosphorylated by this kinase. The transient, dynamic, and unstructured nature of this protein-protein interaction has limited structural mapping of kinase-substrate interfaces. Here, using multiscale MD simulation-based predictions and FRET sensor-based experiments, we investigated the conformational dynamics of the kinase-substrate interface. We found that the binding strength of the kinase-substrate interaction is primarily determined by long-range columbic interactions between basic (Arg/Lys) residues located N-terminally to the phosphorylated Ser/Thr residues in the substrate and by an acidic patch in the kinase catalytic domain. Kinase activity stemmed from conformational flexibility in the region C-terminal to the phosphorylated Ser/Thr residues. Flexibility of the substrate-kinase interaction enabled an Arg/Lys two to three amino acids C-terminal to the phosphorylated Ser/Thr to prime a catalytically active conformation, facilitating phosphoryl transfer to the substrate. The structural mechanisms determining substrate binding and catalytic activity formed the basis of diverse binding affinities and kinase activities of PKCα for 14 substrates with varying degrees of sequence conservation. Our findings provide insight into the dynamic properties of the kinase-substrate interaction that govern substrate binding and turnover. Moreover, this study establishes a modeling and experimental method to elucidate the structural dynamics underlying substrate selectivity among eukaryotic kinases.

ER/K linked GPCR-G protein fusions systematically modulate second messenger response in cells

FRET and BRET approaches are well established for detecting ligand induced GPCR-G protein interactions in cells. Currently, FRET/BRET assays rely on co-expression of GPCR and G protein, and hence depend on the stoichiometry and expression levels of the donor and acceptor probes. On the other hand, GPCR-G protein fusions have been used extensively to understand the selectivity of GPCR signaling pathways. However, the signaling properties of fusion proteins are not consistent across GPCRs. In this study, we describe and characterize novel sensors based on the Systematic Protein Affinity Strength Modulation (SPASM) technique. Sensors consist of a GPCR and G protein tethered by an ER/K linker flanked by FRET probes. SPASM sensors are tested for the β2-, α1-, and α2- adrenergic receptors, and adenosine type 1 receptor (A₁R), tethered to Gαs-XL, Gαi₂, or Gαq subunits. Agonist stimulation of β2-AR and α2-AR increases FRET signal comparable to co-expressed FRET/BRET sensors. SPASM sensors also retain signaling through the endogenous G protein milieu. Importantly, ER/K linker length systematically tunes the GPCR-G protein interaction, with consequent modulation of second messenger signaling for cognate interactions. SPASM GPCR sensors serve the dual purpose of detecting agonist-induced changes in GPCR-G protein interactions, and linking these changes to downstream signaling.

Actin turnover maintains actin filament homeostasis during cytokinetic ring contraction

Many cytokinetic actomyosin ring components undergo dynamic turnover, but its function is unclear. Chew et al. show that continuous actin polymerization ensures crucial F-actin homeostasis during ring contraction, without which ring proteins organize into noncontractile clusters.

Cytokinesis in many eukaryotes involves a tension-generating actomyosin-based contractile ring. Many components of actomyosin rings turn over during contraction, although the significance of this turnover has remained enigmatic. Here, using Schizosaccharomyces japonicus, we investigate the role of turnover of actin and myosin II in its contraction. Actomyosin ring components self-organize into ∼1-µm-spaced clusters instead of undergoing full-ring contraction in the absence of continuous actin polymerization. This effect is reversed when actin filaments are stabilized. We tested the idea that the function of turnover is to ensure actin filament homeostasis in a synthetic system, in which we abolished turnover by fixing rings in cell ghosts with formaldehyde. We found that these rings contracted fully upon exogenous addition of a vertebrate myosin. We conclude that actin turnover is required to maintain actin filament homeostasis during ring contraction and that the requirement for turnover can be bypassed if homeostasis is achieved artificially.

Green synthesis of magnetic Fe3O4 nanoparticles using Couroupita guianensis Aubl. fruit extract for their antibacterial and cytotoxicity activities

In the present study, a sustainable green chemistry approach was established to fabricate magnetic Fe₃O₄ nanoparticles (Fe₃O₄NPs) using the aqueous fruit extract of edible C. guianensis (CGFE). Synthesized NPs were further confirmed with different high-throughput characterization techniques such as UV-visible spectroscopy, FT-IR, XPS, DLS and zeta potential analysis. Additionally, XRD, AFM, HRTEM and SQUID VSM demonstrate the generation of crystalline CGFe₃O₄NPs with mean diameter of 17 ± 10 nm. Interestingly, CGFe₃O₄NPs exhibit a stupendous bactericidal action against different human pathogens which depicts its antimicrobial value. A significant dose-dependent cytotoxic effect of CGFe₃O₄NPs was noticed against treated human hepatocellular carcinoma cells (HepG2).

The GCaMP-R Family of Genetically Encoded Ratiometric Calcium Indicators

We report on GCaMP-Rs, a new family of genetically encoded ratiometric calcium indicators that extend the virtues of the GCaMP proteins to ratiometric measurements. We have engineered a tandem construct of calcium-dependent GCaMP and calcium-independent mCherry fluorescent proteins. The tandem design assures that the two proteins localize in the same cellular compartment(s) and facilitates pixelwise ratiometric measurements; however, Förster resonance energy transfer (FRET) between the fluorophores reduces brightness of the sensor by up to half (depending on the GCaMP variant). To eliminate FRET, we introduced a rigid α-helix, the ER/K helix, between GCaMP and mCherry. Avoiding FRET significantly increases the brightness (notably, even at low calcium concentrations), the signal-to-noise ratio, and the dynamic range.

The DRY motif and the four corners of the cubic ternary complex model

Recent structural data on GPCRs using a variety of spectroscopic approaches suggest that GPCRs adopt a dynamic conformational landscape, with ligands stabilizing subsets of these states to activate one or more downstream signaling effectors. A key outstanding question posed by this emerging dynamic structural model of GPCRs is what states, active, inactive, or intermediate are captured by the numerous crystal structures of GPCRs complexed with a variety of agonists, partial agonists, and antagonists. In the early nineties the discovery of inverse agonists and constitutive activity led to the idea that the active receptor state (R^⁎) is an intrinsic property of the receptor itself rather than of the RG complex, eventually leading to the formulation of the cubic ternary complex model (CTC). Here, by a careful analysis of a series of data obtained with a number of mutants of the highly conserved E/DRY motif, we show evidences for the existence of all the receptor states theorized by the CTC, four 'uncoupled (R, R^⁎ and HR and HR^⁎), and, consequently four 'coupled' (RG, R^⁎G, HRG and HR^⁎G). The E/DRY motif located at the cytosolic end of transmembrane helix III of Class A GPCRs has been widely studied and analyzed because it forms a network of interactions believed to lock receptors in the inactive conformation (R), and, thus, to play a key role in receptor activation. Our conclusions are supported by recent crystal and NMR spectra, as well as by results obtained with two prototypical GPCRs using a new FRET technology that de-couples G protein binding to the receptor from signal transduction. Thus, despite its complexity and limitations, we propose that the CTC is a useful framework to reconcile pharmacological, biochemical and structural data.

The Role of Regulatory Domains in Maintaining Autoinhibition in the Multidomain Kinase PKCα

Resolving the conformational dynamics of large multidomain proteins has proven to be a significant challenge. Here we use a variety of techniques to dissect the roles of individual protein kinase Cα (PKCα) regulatory domains in maintaining catalytic autoinhibition. We find that whereas the pseudosubstrate domain is necessary for autoinhibition it is not sufficient. Instead, each regulatory domain (C1a, C1b, and C2) appears to strengthen the pseudosubstrate-catalytic domain interaction in a nucleotide-dependent manner. The pseudosubstrate and C1a domains, however, are minimally essential for maintaining the inactivated state. Furthermore, disrupting known interactions between the C1a and other regulatory domains releases the autoinhibited interaction and increases basal activity. Modulating this interaction between the catalytic and regulatory domains reveals a direct correlation between autoinhibition and membrane translocation following PKC activation.

Calcium Stimulates Self-Assembly of Protein Kinase C α In Vitro

Protein kinase C α (PKCα) is a nodal regulator in several intracellular signaling networks. PKCα is composed of modular domains that interact with each other to dynamically regulate spatial-temporal function. We find that PKCα specifically, rapidly and reversibly self-assembles in the presence of calcium in vitro. This phenomenon is dependent on, and can be modulated by an intramolecular interaction between the C1a and C2 protein domains of PKCα. Next, we monitor self-assembly of PKC—mCitrine fusion proteins using time-resolved and steady-state homoFRET. HomoFRET between full-length PKCα molecules is observed when in solution with both calcium and liposomes containing either diacylglycerol (DAG) or phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂). Surprisingly, the C2 domain is sufficient to cluster on liposomes containing PI(4,5)P₂, indicating the C1a domain is not required for self-assembly in this context. We conclude that three distinct clustered states of PKCα can be formed depending on what combination of cofactors are bound, but Ca²⁺ is minimally required and sufficient for clustering.

Engineering Circular Gliding of Actin Filaments Along Myosin-Patterned DNA Nanotube Rings To Study Long-Term Actin-Myosin Behaviors

Nature has evolved molecular motors that are critical in cellular processes occurring over broad time scales, ranging from seconds to years. Despite the importance of the long-term behavior of molecular machines, topics such as enzymatic lifetime are underexplored due to the lack of a suitable approach for monitoring motor activity over long time periods. Here, we developed an "O"-shaped Myosin Empowered Gliding Assay (OMEGA) that utilizes engineered micron-scale DNA nanotube rings with precise arrangements of myosin VI to trap gliding actin filaments. This circular gliding assay platform allows the same individual actin filament to glide over the same myosin ensemble (50-1000 motors per ring) multiple times. First, we systematically characterized the formation of DNA nanotubes rings with 4, 6, 8, and 10 helix circumferences. Individual actin filaments glide along the nanotube rings with high processivity for up to 12.8 revolutions or 11 min in run time. We then show actin gliding speed is robust to variation in motor number and independent of ring curvature within our sample space (ring diameter of 0.5-4 μm). As a model application of OMEGA, we then analyze motor-based mechanical influence on "stop-and-go" gliding behavior of actin filaments, revealing that the stop-to-go transition probability is dependent on motor flexibility. Our circular gliding assay may provide a closed-loop platform for monitoring long-term behavior of broad classes of molecular motors and enable characterization of motor robustness and long time scale nanomechanical processes.