Open State Research Articles

STUDY OF CONDITIONING EFFECT OF BALL VALVES

Two or more configurations are combined to provide common use of ball valves. The use of metal fasteners in ball valves is used to ensure tightness under conditions of high temperature and pressure. Studies conducted on connecting structures show that 70% of them fail due to problems of fixation. With the application of a magnetic device, the position of the connectors is different in the open and closed state of the faucet. In the open state of the faucet, the magnetic force does not affect the connectors. This, in turn, minimizes the friction that may arise in the coupling elements in the ball-coupling pair. The correct design of fastening systems is an important factor for efficient and reliable operation. Methodologies range from simple computation-based procedures to detailed mathematical models. An appropriate mathematical model for the design and analysis of a crane provides a logical equivalent determined by the characteristics of the system. The design methodology offers a number of innovations for the identification of all possible system configurations capable of meeting a specific requirement according to the required levels of reliability. Keywords: ball valve, metal fitting, magnetic device.

Binding kinetics of quaternary ammonium ions in Kcv potassium channels.

Kcv channels from plant viruses represent the autonomous pore module of potassium channels, devoid of any regulatory domains. These small proteins show very reproducible single-channel behavior in planar lipid bilayers. Thus, they are an optimum system for the study of the biophysics of ion transport and gating. Structural models based on homology modeling have been used successfully, but experimental structural data are currently not available. Here we determine the size of the cytosolic pore entrance by studying the blocker kinetics. Blocker binding and dissociation rate constants ranging from 0.01 to 1000 ms-1 were determined for different quaternary ammonium ions. We found that the cytosolic pore entrance of KcvNTS must be at least 11 Å wide. The results further indicate that the residues controlling a cytosolic gate in one of the Kcv isoforms influence blocker binding/dissociation as well as a second gate even when the cytosolic gate is in the open state. The voltage dependence of the rate constant of blocker release is used to test, which blockers bind to the same binding site.

A regulatory module mediating temperature control of cell-cell communication facilitates tree bud dormancy release

The control of cell–cell communication via plasmodesmata (PD) plays a key role in plant development. In tree buds, low-temperature conditions (LT) induce a switch in plasmodesmata from a closed to an open state, which restores cell-to-cell communication in the shoot apex and releases dormancy. Using genetic and cell-biological approaches, we have identified a previously uncharacterized transcription factor, Low-temperature-Induced MADS-box 1 (LIM1), as an LT-induced, direct upstream activator of the gibberellic acid (GA) pathway. The LIM1-GA module mediates low temperature-induced plasmodesmata opening, by negatively regulating callose accumulation to promote dormancy release. LIM1 also activates expression of FT1 (FLOWERING LOCUS T), another LT-induced factor, with LIM1-FT1 forming a coherent feedforward loop converging on low-temperature regulation of gibberellin signaling in dormancy release. Mathematical modeling and experimental validation suggest that negative feedback regulation of LIM1 by gibberellin could play a crucial role in maintaining the robust temporal regulation of bud responses to low temperature. These results reveal genetic factors linking temperature control of cell–cell communication with regulation of seasonally-aligned growth crucial for adaptation of trees.

Investigation of the sound insulation and natural ventilation performance of a metamaterial-based open window

Recent advancements in metamaterials have created new opportunities to enhance indoor environmental quality (IEQ) by integrating natural ventilation and sound insulation in architectural designs. Metamaterial-based windows can facilitate natural ventilation, contributing to energy savings while also protecting against outdoor noise. However, international standards for assessing façade sound insulation typically assume all partitions are closed, with only the Danish standard DS 447:2021 accounting for partially open conventional windows. These standards do not address simultaneous noise mitigation and natural ventilation. To fill this gap, this study evaluated a prototype metamaterial-based device called the Acoustic Metawindow (AMW) unit using three experimental methods. These methods included the diffuse field method (ISO 10140 series), an adapted directive sound field method (EN 1793-6), and beamforming to control sound leakages from the AMW unit in both closed and open states. Additionally, the study used an adapted ISO 9972 method to assess the ventilation potential alongside sound insulation of the open AMW unit. The findings revealed that the AMW unit significantly outperformed equivalently open windows, achieving a sound level difference (Dn,e) improvement of 5–15 dB in the 500–5000 Hz frequency range, resulting in a total Dn,e,w of 30 dB. The study also indicated a correlation between the frequency range of effective sound insulation and the metamaterial design features of the AMW unit. This research suggests the possibility of a more inclusive standard that considers partially open sound-insulating devices as windows in the built environment, combining noise mitigation and energy saving.

RNA m5C oxidation by TET2 regulates chromatin state and leukaemogenesis

Mutation of tet methylcytosine dioxygenase 2 (encoded by TET2) drives myeloid malignancy initiation and progression1–3. TET2 deficiency is known to cause a globally opened chromatin state and activation of genes contributing to aberrant haematopoietic stem cell self-renewal4,5. However, the open chromatin observed in TET2-deficient mouse embryonic stem cells, leukaemic cells and haematopoietic stem and progenitor cells5 is inconsistent with the designated role of DNA 5-methylcytosine oxidation of TET2. Here we show that chromatin-associated retrotransposon RNA 5-methylcytosine (m5C) can be recognized by the methyl-CpG-binding-domain protein MBD6, which guides deubiquitination of nearby monoubiquitinated Lys119 of histone H2A (H2AK119ub) to promote an open chromatin state. TET2 oxidizes m5C and antagonizes this MBD6-dependent H2AK119ub deubiquitination. TET2 depletion thereby leads to globally decreased H2AK119ub, more open chromatin and increased transcription in stem cells. TET2-mutant human leukaemia becomes dependent on this gene activation pathway, with MBD6 depletion selectively blocking proliferation of TET2-mutant leukaemic cells and largely reversing the haematopoiesis defects caused by Tet2 loss in mouse models. Together, our findings reveal a chromatin regulation pathway by TET2 through retrotransposon RNA m5C oxidation and identify the downstream MBD6 protein as a feasible target for developing therapies specific against TET2 mutant malignancies.

The fully activated open state of KCNQ1 controls the cardiac "fight-or-flight" response.

The cardiac KCNQ1 + KCNE1 (IKs) channel regulates heart rhythm under both normal and stress conditions. Under stress, the β-adrenergic stimulation elevates the intracellular cyclic adenosine monophosphate (cAMP) level, leading to KCNQ1 phosphorylation by protein kinase A and increased IKs, which shortens action potentials to adapt to accelerated heart rate. An impaired response to the β-adrenergic stimulation due to KCNQ1 mutations is associated with the occurrence of a lethal congenital long QT syndrome (type 1, also known as LQT1). However, the underlying mechanism of β-adrenergic stimulation of IKs remains unclear, impeding the development of new therapeutics. Here, we find that the unique properties of KCNQ1 channel gating with two distinct open states are key to this mechanism. KCNQ1's fully activated open (AO) state is more sensitive to cAMP than its intermediate open state. By enhancing the AO state occupancy, the small molecules ML277 and C28 are found to effectively enhance the cAMP sensitivity of the KCNQ1 channel, independent of KCNE1 association. This finding of enhancing AO state occupancy leads to a potential novel strategy to rescue the response of IKs to β-adrenergic stimulation in LQT1 mutants. The success of this approach is demonstrated in cardiac myocytes and also in a high-risk LQT1 mutation. In conclusion, the present study not only uncovers the key role of the AO state in IKs channel phosphorylation, but also provides a target for antiarrhythmic strategy.

Linear-acoustic effects of asymmetrical undercutting of toneholes of woodwind instruments.

The influence of the presence and magnitude of asymmetrical undercutting of the toneholes of woodwind instruments on the change in their effective radius and the corresponding shift of the eigenfrequencies of the air duct is considered. Within the framework of the electro-acoustic analogy, a tonehole with an asymmetrical undercutting along the axis of the main bore is presented as a cascade connection of two holes with different radii (undercutting and not undercutting parts of the hole), and with a sideway undercutting-in the form of a parallel connection. Formulas for numerical calculations are given that make it possible to determine the effective radius of such holes for the open state in the low-frequency approximation. Based on the obtained dependencies, using the transmission-matrix method, the eigenfrequencies of an air duct with one hole were calculated and compared with the results of computer modeling in the COMSOL Multiphysics 5.6 program. It is shown that increasing the degree and angle of undercutting leads to an increase in the effective radius, a displacement of the "center of gravity" of the sound hole along the main bore axis, and has effect on the shift of resonant frequency.

On the function of TRAP substrate-binding proteins: Conformational variation of the sialic acid binding protein SiaP

Tripartite ATP-independent periplasmic (TRAP) transporters are analogous to ABC transporters in that they use a substrate-binding protein to scavenge metabolites (e.g., N-acetylneuraminate) and deliver them to the membrane components for import. TRAP substrate-binding proteins are thought to bind the substrate using a two-state (open and closed) induced-fit mechanism. We solved the structure of the TRAP N-acetylneuraminate substrate-binding protein from Aggregatibacter actinomycetemcomitans (AaSiaP) in both the open ligand-free and closed liganded conformations. Surprisingly, we also observed an intermediate conformation, where AaSiaP is mostly closed and is bound to a non-cognate ligand, acetate, which hints at how N-acetylneuraminate binding stabilises a fully closed state. AaSiaP preferentially binds N-acetylneuraminate (KD = 0.4 μM) compared to N-glycolylneuraminate (KD = 4.4 μM), which is explained by the closed-N-acetylneuraminate bound structure. Small-angle X-ray scattering data alongside molecular dynamics simulations suggest the AaSiaP adopts a more open state in solution than in crystal. However, the open unliganded conformation can also sample closed conformations. Molecular dynamics simulations also demonstrate the importance of water molecules for stabilising the closed conformation. Although our data is consistent with an induced fit model of binding, we suggest that the open unliganded conformation may sample multiple states capable of binding substrate. The mechanism by which the ligand is released for import remains to be determined.

Uncovering conserved networks and global conformational changes in G protein-coupled receptor kinases

G protein-coupled receptor kinases (GRKs) are essential regulators of signaling pathways mediated by G protein-coupled receptors. Recent research suggests that GRK-mediated phosphorylation patterns dictate functional selectivity, leading to biased cellular responses. However, a comprehensive understanding of the structural mechanisms at the single-residue level remains elusive. This study aims to define the general conformational dynamics of GRKs with a particular focus on quantifying the transitions between the closed and open states. Specifically, we examined these transitions, classified based on the ionic lock between the regulatory G protein signaling homology domain and kinase domain. To facilitate a precise structural comparison, we assigned common labels to topologically identical positions across the 47 GRK structures retrieved from the Protein Data Bank. Our analysis identified both general and subfamily-specific dynamic movements within the networks and measured the conformational change scores between the two states. Elucidating these structural dynamics could provide significant insights into the regulatory mechanisms of GRK.

Structural basis for translational control by the human 48S initiation complex.

The selection of an open reading frame (ORF) for translation of eukaryotic mRNA relies on remodeling of the scanning 48S initiation complex into an elongation-ready 80S ribosome. Using cryo-electron microscopy, we visualize the key commitment steps orchestrating 48S remodeling in humans. The mRNA Kozak sequence facilitates mRNA scanning in the 48S open state and stabilizes the 48S closed state by organizing the contacts of eukaryotic initiation factors (eIFs) and ribosomal proteins and by reconfiguring mRNA structure. GTPase-triggered large-scale fluctuations of 48S-bound eIF2 facilitate eIF5B recruitment, transfer of initiator tRNA from eIF2 to eIF5B and the release of eIF5 and eIF2. The 48S-bound multisubunit eIF3 complex controls ribosomal subunit joining by coupling eIF exchange to gradual displacement of the eIF3c N-terminal domain from the intersubunit interface. These findings reveal the structural mechanism of ORF selection in human cells and explain how eIF3 could function in the context of the 80S ribosome.

Exploring Protonation State, Ion Binding, and Photoactivated Channel Opening of an Anion Channelrhodopsin by Molecular Simulations.

Channelrhodopsins are light-gated ion channels with a retinal chromophore found in microbes and are widely used in optogenetics, a field of neuroscience that utilizes light to regulate neuronal activity. GtACR1, an anion conducting channelrhodopsin derived from Guillardia theta, has attracted attention for its application as a neuronal silencer in optogenetics because of its high conductivity and selectivity. However, atomistic mechanisms of channel photoactivation and ion conduction have not yet been elucidated. In the present study, we investigated the molecular characteristics of GtACR1 and its photoactivation processes by molecular simulations. The QM/MM RWFE-SCF method which combines highly accurate quantum chemistry calculations with long-time molecular dynamics (MD) simulations were used to model protein structures of the wild-type and mutants with different protonation states of key groups and to calculate absorption energies for verification of the models. The QM/MM modeling together with MD simulations of free-energy calculations favors protonation of a key counterion carboxyl group of Asp234 with a strong binding of a chloride ion in the extracellular pocket in the dark state. A channel open state was also successfully modeled by the QM/MM RWFE-SCF free-energy optimizations, providing atomistic insights into the channel activation mechanism.

Revealing a hidden conducting state by manipulating the intracellular domains in KV10.1 exposes the coupling between two gating mechanisms.

The KCNH family of potassium channels serves relevant physiological functions in both excitable and non-excitable cells, reflected in the massive consequences of mutations or pharmacological manipulation of their function. This group of channels shares structural homology with other voltage-gated K+ channels, but the mechanisms of gating in this family show significant differences with respect to the canonical electromechanical coupling in these molecules. In particular, the large intracellular domains of KCNH channels play a crucial role in gating that is still only partly understood. Using KCNH1(KV10.1) as a model, we have characterized the behavior of a series of modified channels that could not be explained by the current models. With electrophysiological and biochemical methods combined with mathematical modeling, we show that the uncovering of an open state can explain the behavior of the mutants. This open state, which is not detectable in wild-type channels, appears to lack the rapid flicker block of the conventional open state. Because it is accessed from deep closed states, it elucidates intermediate gating events well ahead of channel opening in the wild type. This allowed us to study gating steps prior to opening, which, for example, explain the mechanism of gating inhibition by Ca2+-Calmodulin and generate a model that describes the characteristic features of KCNH channels gating.

An explanation for the slow-rise phase of solar eruptions

ABSTRACT Solar eruptions are sudden release of the magnetic free energy accumulated within a quasi-static evolutionary process of the corona. Interestingly, many solar eruptions are preceded by a short-term slow-rise phase, during which the pre-eruption structure rises at a speed significantly larger than that of the quasi-static evolution. Here we suggest an explanation for the slow-rise phase based on a recent high-accuracy magnetohydrodynamic simulation for initiation of solar eruption. The simulation shows that by continuously shearing a bipolar magnetic arcade, an internal current sheet forms gradually, and an eruption begins once magnetic reconnection is triggered at the current sheet. We find in the simulation that the overlying field presents a slow-rise phase before the reconnection sets in. In addition, the rising speed is significantly larger than that of the core field during this phase. This slow rise is a manifestation of the growing expansion of the arcade in the process of approaching a fully open field state, which is inherent to the formation of a current sheet before the eruption. We also show three flare events with slow-rise phases that are highly consistent with these key characteristics in the simulation: an expansion of the overlying coronal loops with speeds much larger than the quasi-static evolution speed, and for those events with filament eruption, the slow rise of filament is much smaller than that of the overlying loops. In this type of events, the eruption might be initiated through the mechanism as shown in the simulation, and the expansion of overlying coronal loops is a better indicator of the slow-rise phase.

Finely ordered intracellular domain harbors an allosteric site to modulate physiopathological function of P2X3 receptors

P2X receptors, a subfamily of ligand-gated ion channels activated by extracellular ATP, are implicated in various physiopathological processes, including inflammation, pain perception, and immune and respiratory regulations. Structural determinations using crystallography and cryo-EM have revealed that the extracellular three-dimensional architectures of different P2X subtypes across various species are remarkably identical, greatly advancing our understanding of P2X activation mechanisms. However, structural studies yield paradoxical architectures of the intracellular domain (ICD) of different subtypes (e.g., P2X3 and P2X7) at the apo state, and the role of the ICD in P2X functional regulation remains unclear. Here, we propose that the P2X3 receptor’s ICD has an apo state conformation similar to the open state but with a less tense architecture, containing allosteric sites that influence P2X3’s physiological and pathological roles. Using covalent occupancy, engineered disulfide bonds and voltage-clamp fluorometry, we suggested that the ICD can undergo coordinated motions with the transmembrane domain of P2X3, thereby facilitating channel activation. Additionally, we identified a novel P2X3 enhancer, PSFL77, and uncovered its potential allosteric site located in the 1α3β domain of the ICD. PSFL77 modulated pain perception in P2rx3+/+, but not in P2rx3−/−, mice, indicating that the 1α3β, a “tunable” region implicated in the regulation of P2X3 functions. Thus, when P2X3 is in its apo state, its ICD architecture is fairly ordered rather than an unstructured outward folding, enabling allosteric modulation of the signaling of P2X3 receptors.

Reliability analysis of output electrical response performance of multi-state flexoelectric structures under single and multiple failure modes

This paper proposes a reliability model of flexoelectric beams in the electrical open and short circuit states when different failure modes and the multiple failure modes of the output electrical response performances are considered, respectively. The reliability indices of the flexoelectric beams in the two circuit states can be defined based on the output electrical response models. Sequentially, the importance sampling (IS) and the mixed importance sampling (IS) methods are respectively used to calculate the reliability of the flexoelectric beams in single and multiple failure modes. The reliability results of the flexoelectric beams are verified by comparing them with the results of the Monte Carlo Simulation (MCS). The numerical results show that the flexoelectric beam is entered into a relatively safe and reliable state when the critical value of the open circuit voltage of 0.235 V and the thickness of the flexoelectric beams of 1 mm are considered as well as the length-thickness ratio of 20.

In Vivo Three-Dimensional Geometric Reconstruction of the Mouse Aortic Heart Valve.

Aortic valve (AV) disease is a common valvular lesion in the United States, present in about 5% of the population at age 65 with increasing prevalence with advancing age. While current replacement heart valves have extended life for many, their long-term use remains hampered by limited durability. Non-surgical treatments for AV disease do not yet exist, in large part because our understanding of AV disease etiology remains incomplete. The direct study of human AV disease remains hampered by the fact that clinical data is only available at the time of treatment, where the disease is at or near end stage and any time progression information has been lost. Large animal models, long used to assess replacement AV devices, cannot yet reproduce AV disease processes. As an important alternative mouse animal models are attractive for their ability to perform genetic studies of the AV disease processes and test potential pharmaceutical treatments. While mouse models have been used for cellular and genetic studies of AV disease, their small size and fast heart rates have hindered their use for tissue- and organ-level studies. We have recently developed a novel ex vivo micro-CT-based methodology to 3D reconstruct murine heart valves and estimate the leaflet mechanical behaviors (Feng et al. in Sci Rep 13(1):12852, 2023). In the present study, we extended our approach to 3D reconstruction of the in vivo functional murine AV (mAV) geometry using high-frequency four-dimensional ultrasound (4DUS). From the resulting 4DUS images we digitized the mAV mid-surface coordinates in the fully closed and fully opened states. We then utilized matched high-resolution µCT images of ex vivo mouse mAV to develop mAV NURBS-based geometric model. We then fitted the mAV geometric model to the in vivo data to reconstruct the 3D in vivo mAV geometry in the closed and open states in n = 3 mAV. Results demonstrated high fidelity geometric results. To our knowledge, this is the first time such reconstruction was ever achieved. This robust assessment of in vivo mAV leaflet kinematics in 3D opens up the possibility for longitudinal characterization of murine models that develop aortic valve disease.

Mad honey (wild honey) poisoning: clinical case series from Nepal.

Mad honey is commonly used for hypertension, and coronary artery disease, and as a sexual stimulant. Patients with mad honey poisoning present with dizziness, nausea, syncope, blurred vision, bradycardia, and hypotension with ECG findings of sinus bradycardia, complete AV block, and ST elevation. Here, the authors report five cases admitted to our tertiary care center following the consumption of mad honey. The amount of ingestion of honey varies from 1 to 2 teaspoons (~10-20ml). Most of the cases presented with chief complaints of nausea, dizziness, and vomiting, and all the cases had hypotension and bradycardia. Two cases were admitted to the ward and three of them were admitted to the ICU for further management. They were managed with intravenous fluid, injection atropine along with adjunctive vasopressor and oxygen whenever necessary. Mad honey contains grayanotoxin extracted from the nectar of Rhododendron species. This honey contains grayanotoxin, which binds to sodium channels in its open state causing hyperpolarization of the sodium channel predominantly causing gastrointestinal, neurological, and respiratory symptoms. Intravenous fluids and injection atropine are the mainstays of management in an ICU setup. Some also may require vasopressors. Mad honey poisoning is rare, and limited cases have been reported in Nepal. Physicians should consider mad honey poisoning in cases with ingestion history and clinical symptoms, as it may be a clinical diagnosis due to limited lab tests for grayanotoxin intoxication. Supportive management still forms the cornerstone for its management after diagnosis.

Structural insight into the Arabidopsis vacuolar anion channel ALMT9 shows clade specificity

The Arabidopsis thaliana aluminum-activated malate transporter 9 (AtALMT9) functions as a vacuolar chloride channel that regulates the stomatal aperture. Here, we present the cryoelectron microscopy (cryo-EM) structures of AtALMT9 in three distinct states. AtALMT9 forms a dimer, and the pore is lined with four positively charged rings. The apo-AtALMT9 state shows a putative endogenous citrate obstructing the pore, where two W120 constriction residues enclose a gate with a pore radius of approximately 1.8Å, representing an open state. Interestingly, channel closure is solely controlled by W120. Compared to wild-type plants, the W120A mutant exhibits more sensitivity to drought stress and is unable to restore the visual phenotype on leaves upon water recovery, reflecting persistent stomatal opening. Furthermore, notable variations are noted in channel gating and substrate recognition of Glycine max ALMT12, AtALMT9, and AtALMT1. In summary, our investigation enhances comprehension of the interplay between structure and function within the ALMT family.

Thermoring basis for heat unfolding‐induced inactivation in TRPV1

AbstractTransient receptor potential vanilloid‐1 (TRPV1) is a capsaicin receptor that employs use‐dependent desensitization to protect highly evolved mammals from noxious heat damage in response to repeated or constant heat stimuli. However, the underlying structural factor or motif has not been precisely resolved. In this computational study, the graph theory‐based grid thermodynamic model was used to reveal how temperature‐dependent noncovalent interactions, as identified in the 3D structures of rat TRPV1, could develop a well‐organized fluidic grid‐like mesh network. This network features various topological grids constrained as thermosensitive rings that range in size from the biggest to the smallest, governing distinct structural and functional traits of the channel in response to different temperature degrees. After discovering that heat unfolding of three specific biggest grids, one in the closed state and two in the open state, respectively, causes the reversible activation at 43°C and thermal inactivation between 56°C and 61°C, a smaller random grid was also found to be responsible for irreversible inactivation and use‐dependent desensitization from the pre‐open closed state within the temperature range of 43°C–61°C. Thus, these two distinct inactivation pathways of TRPV1 may be involved in protecting those mammals against noxious heat damage.Key Points A perturbation at the protein–water interface was accompanied by partial heat or cold unfolding of the membrane protein. A reversible or irreversible gating transition of an ion channel may result from a specific or random interaction between two active sites, respectively. Kinetically driven protein aggregation was not the cause of thermodynamically trapped irreversible inactivation, but rather a later stage of partial heat‐induced unfolding.

PH-Responsive Rhodamine Nanotube Capable of Self-Reporting the Assembly State.

Nanomaterials that respond to intracellular signals, such as pH, have the potential for many biomedical applications, such as drug delivery, because the assembly/disassembly process can be tailored to respond to a stimulus characteristic of a specific subcellular location. In this work, two rhodamine-peptides that form stable nanotubes at physiological pH but dissociate into highly fluorescent monomers within the acidified interior of endosomal/lysosomal cellular compartments have been developed. The rhodamine dipeptide conjugates, NH2-KK(RhB)-NH2 (RhB-KK) and NH2-EK(RhB)-NH2 (RhB-KE) with rhodamine B chromophores appended at the ε-amino position of a lysine residue, were shown to assemble into well-defined nanotubes at pH values above ∼4-5 and to dissociate into a fluorescent monomer state at lower pH values. The pH dependence of the assembly process was investigated using circular dichroism (CD) and fluorescence spectroscopy along with transmission electron microscopy (TEM), atomic force microscopy (AFM), and confocal imaging. Although the ring opening/closing transition of the rhodamine chromophore took place at pH 4.1 for both peptides, the onset of assembly began at pH 4.6 for RhB-KE and at a comparatively more basic pH (5.8) for RhB-KK. Accordingly, the rhodamine-peptides interconverted between three pH-dependent states: an open-ring, monomeric state (λmax 580 nm, λex 550 nm) at pH values at or below ∼4.6; a closed-ring, nanotube form that exhibits AIEE (λmax 460 nm, λex = 330 nm) at higher pH values; a closed-ring, nonemissive monomeric state that emerged below the critical micelle concentrations (CMC). The pH-responsive features of the peptides were evaluated by live-cell imaging in three cancer cell lines using confocal laser scanning microscopy (CLSM). Visualizing the cells after incubation with either RhB-KE or RhB-KK produced CLSM images with a punctate appearance in the Texas Red channel that colocalized with the lysosomes. These experiments indicate that the nanotubes were rapidly trafficked into the acidic lysosomal compartments within the cells, which induced dissociation into a monomeric, open state. Uptake inhibition studies suggested that cellular uptake was mediated by either caveolae- or clathrin-mediated endocytosis, depending on the cell line studied.