Whether class-A G-protein coupled receptors (GPCRs) exist and work as monomers or dimers has drawn extensive attention. A class-A GPCR dopamine D2 receptor (D2R) is involved in many physiological and ...pathological processes and diseases, indicating its critical role in proper functioning of neuronal circuits. In particular, D2R homodimers might play key roles in schizophrenia development and amphetamine-induced psychosis. Here, using single-molecule imaging, we directly tracked single D2R molecules in the plasma membrane at a physiological temperature of 37 °C, and unequivocally determined that D2R forms transient dimers with a lifetime of 68 ms in its resting state. Agonist addition prolonged the dimer lifetime by a factor of ~1.5, suggesting the possibility that transient dimers might be involved in signaling.
Eight years after the Fukushima nuclear accident, mosses exposed in bags were used to investigate their ability to accumulate radiocaesium and therefore to act as biointerceptors of 134Cs and 137Cs ...in the evacuated area of the Fukushima territory. Bags were filled with 3 widely studied moss species (Sphagnum palustre, Hypnum cupressiforme, and Hypnum plumaeforme) and exposed for 3, 6 or 9 weeks at 5 former residential sites within the Fukushima area and, for comparison, at three background sites located 700 km away. The radiocaesium activity concentrations found in moss bags were evaluated as function of exposure time, site conditions and moss species. In the Fukushima area, the moss bags accumulated 137Cs at all exposure sites and in all exposure periods, with S. palustre having the highest 137Cs accumulation ability. The 137Cs activity concentrations (from 28 to 4700 Bq kg−1) measured in moss bags increased with the exposure time and were consistent with the decontamination status of each exposure site, highlighting the big potential of moss bags to discriminate among exposure sites. Time dependency of 137Cs activity concentrations measured in mosses allowed the calculation of location-specific and species-specific factors, which can be used to predict radiocaesium accumulation trends in future biomonitoring surveys performed in the same area with the same experimental design. Autoradiography and electron microscopy analyses of the moss surfaces revealed a prevalence of soil-derived particulate form of radiocaesium, suggesting the use of moss bags as warning sensors of resuspended particles potentially harmful for local residents.
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•Mosses in bags act as biosensors of radiocaesium in evacuated Fukushima municipalities.•In Fukushima sites moss-bags highlight 137Cs after only 3 weeks of exposure.•Sphagnum palustre shows the highest 137Cs uptake ability.•Radiocaesium occurs on moss surfaces in soil-derived particulate form.•Location (LF) and Species (SF) factors may help to determine 137Cs accumulation trends.
Many plasma membrane (PM) functions depend on the cholesterol concentration in the PM in strikingly nonlinear, cooperative ways: fully functional in the presence of physiological cholesterol levels ...(35~45 mol%), and nonfunctional below 25 mol% cholesterol; namely, still in the presence of high concentrations of cholesterol. This suggests the involvement of cholesterol‐based complexes/domains formed cooperatively. In this review, by examining the results obtained by using fluorescent lipid analogs and avoiding the trap of circular logic, often found in the raft literature, we point out the fundamental similarities of liquid‐ordered (Lo)‐phase domains in giant unilamellar vesicles, Lo‐phase‐like domains formed at lower temperatures in giant PM vesicles, and detergent‐resistant membranes: these domains are formed by cooperative interactions of cholesterol, saturated acyl chains, and unsaturated acyl chains, in the presence of >25 mol% cholesterol. The literature contains evidence, indicating that the domains formed by the same basic cooperative molecular interactions exist and play essential roles in signal transduction in the PM. Therefore, as a working definition, we propose that raft domains in the PM are liquid‐like molecular complexes/domains formed by cooperative interactions of cholesterol with saturated acyl chains as well as unsaturated acyl chains, due to saturated acyl chains' weak multiple accommodating interactions with cholesterol and cholesterol's low miscibility with unsaturated acyl chains and TM proteins. Molecules move within raft domains and exchange with those in the bulk PM. We provide a logically established collection of fluorescent lipid probes that preferentially partition into raft and non‐raft domains, as defined here, in the PM.
A working definition of raft domains in the plasma membrane (PM) is proposed, based on cooperative interactions of cholesterol with saturated acyl chains as well as unsaturated acyl chains, found in giant unilamellar vesicles, giant PM vesicles, which resemble the PMs after the removal of the actin‐based membrane skeleton, cold‐detergent‐treated PMs, and single‐molecule imaging data obtained in the PM. Furthermore, we provide a logically established list of fluorescent lipid probes that preferentially partition into raft/non‐raft domains in the PM.
The bursting activity of pancreatic β cells is correlated with insulin secretion. Although normal pancreatic β cells show periodic bursting, the bursting activity becomes irregular in dysfunctional ...pancreatic β cells of type 2 diabetic patients. In this study, we modeled the dynamics of dysfunctional pancreatic β cells using differential equations. We investigated it in terms of energy efficiency of control. The control method is considered for on-demand electrical stimulation using the methodology of chaos control. Numerical simulation results show that the bursts are controlled in a periodic rhythm by the feedback mechanism. In addition, we found input timings that induce energy efficient control for rhythmic bursts. These results suggest that chaos control can improve insulin secretion, which might contribute to type 2 diabetes treatment.
Receptor dimerization is important for many signaling pathways. However, the monomer-dimer equilibrium has never been fully characterized for any receptor with a 2D equilibrium constant as well as ...association/dissociation rate constants (termed super-quantification). Here, we determined the dynamic equilibrium for the N-formyl peptide receptor (FPR), a chemoattractant G protein-coupled receptor (GPCR), in live cells at 37°C by developing a single fluorescent-molecule imaging method. Both before and after liganding, the dimer-monomer 2D equilibrium is unchanged, giving an equilibrium constant of 3.6 copies/μm², with a dissociation and 2D association rate constant of 11.0 s⁻¹ and 3.1 copies/μm²s⁻¹, respectively. At physiological expression levels of ~2.1 receptor copies/μm² (~6,000 copies/cell), monomers continually convert into dimers every 150 ms, dimers dissociate into monomers in 91 ms, and at any moment, 2,500 and 3,500 receptor molecules participate in transient dimers and monomers, respectively. Not only do FPR dimers fall apart rapidly, but FPR monomers also convert into dimers very quickly.
Based on recent single-molecule imaging results in the living cell plasma membrane, we propose a hierarchical architecture of three-tiered mesoscale (2–300
nm) domains to represent the fundamental ...functional organization of the plasma membrane: (i) membrane compartments of 40–300
nm in diameter due to the partitioning of the entire plasma membrane by the actin-based membrane skeleton ‘fence’ and transmembrane protein ‘pickets’ anchored to the fence; (ii) raft domains (2–20
nm); and (iii) dimers/oligomers and greater complexes of membrane-associated proteins (3–10
nm). The basic molecular interactions required for the signal transduction function of the plasma membrane can be fundamentally understood and conveniently summarized as the cooperative actions of these mesoscale domains, where thermal fluctuations/movements of molecules and weak cooperativity play crucial roles.
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Endothelial cells are known to respond to mechanical forces such as fluid shear stress and cyclic stretch, but elucidating the mechanism for mechanosensing has been difficult. Experimental data ...indicate that there are probably several sensing mechanisms. We have recently proposed a novel mechanoresponse mechanism that involves platelet endothelial cell adhesion molecule‐1 (PECAM‐1). When endothelial cells are stimulated by fluid shear stress, PECAM‐1 is tyrosine phosphorylated and activates the extracellular signal‐regulated kinase 1 and 2 (ERK1/2) signalling cascade. The same signalling events occurred when we applied pulling force directly on PECAM‐1 on the endothelial cell surface using magnetic beads coated with antibodies against the external domain of PECAM‐1. These results appear to indicate that PECAM‐1 is a mechanotransduction molecule. To our knowledge, this is the first mammalian molecule that is shown to respond to mechanical force directly exerted to it.
Sphingomyelin (SM) has been proposed to form cholesterol-dependent raft domains and sphingolipid domains in the plasma membrane (PM). How SM contributes to the formation and function of these domains ...remains unknown, primarily because of the scarcity of suitable fluorescent SM analogs. We developed new fluorescent SM analogs by conjugating a hydrophilic fluorophore to the SM choline headgroup without eliminating its positive charge, via a hydrophilic nonaethylene glycol linker. The new analogs behaved similarly to the native SM in terms of their partitioning behaviors in artificial liquid order-disorder phase-separated membranes and detergent-resistant PM preparations. Single fluorescent molecule tracking in the live-cell PM revealed that they indirectly interact with each other in cholesterol- and sphingosine backbone-dependent manners, and that, for ∼10-50 ms, they undergo transient colocalization-codiffusion with a glycosylphosphatidylinositol (GPI)-anchored protein, CD59 (in monomers, transient-dimer rafts, and clusters), in CD59-oligomer size-, cholesterol-, and GPI anchoring-dependent manners. These results suggest that SM continually and rapidly exchanges between CD59-associated raft domains and the bulk PM.
Advanced single-molecule fluorescent imaging was applied to study the dynamic organization of raft-associated glycosylphosphatidylinositol-anchored proteins (GPI-APs) in the plasma membrane and their ...stimulation-induced changes. In resting cells, virtually all of the GPI-APs are mobile and continually form transient (~200 ms) homodimers (termed homodimer rafts) through ectodomain protein interactions, stabilized by the presence of the GPI-anchoring chain and cholesterol. Heterodimers do not form, suggesting a fundamental role for the specific ectodomain protein interaction. Under higher physiological expression conditions , homodimers coalesce to form hetero- and homo-GPI-AP oligomer rafts through raft-based lipid interactions. When CD59 was ligated, it formed stable oligomer rafts containing up to four CD59 molecules, which triggered intracellular Ca(2+) responses that were dependent on GPI anchorage and cholesterol, suggesting a key part played by transient homodimer rafts. Transient homodimer rafts are most likely one of the basic units for the organization and function of raft domains containing GPI-APs.
The interplay of magnetism and spin-orbit coupling on an Fe kagome lattice in Fe
Sn
crystal produces a unique band structure leading to an order of magnitude larger anomalous Hall effect than in ...conventional ferromagnetic metals. In this work, we demonstrate that Fe-Sn nanocrystalline films also exhibit a large anomalous Hall effect, being applicable to magnetic sensors that satisfy both high sensitivity and thermal stability. In the films prepared by a co-sputtering technique at room temperature, the partial development of crystalline lattice order appears as nanocrystals of the Fe-Sn kagome layer. The tangent of Hall angle, the ratio of Hall resistivity to longitudinal resistivity, is maximized in the optimal alloy composition of close to Fe
Sn
, implying the possible contribution of the kagome origin even though the films are composed of nanocrystal and amorphous-like domains. These ferromagnetic Fe-Sn films possess great advantages as a Hall sensor over semiconductors in thermal stability owing to the weak temperature dependence of the anomalous Hall responses. Moreover, the room-temperature fabrication enables us to develop a mechanically flexible Hall sensor on an organic substrate. These demonstrations manifest the potential of ferromagnetic kagome metals as untapped reservoir for designing new functional devices.
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