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At least 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Ca2+ Effects on Fe(II) Interactions with Mn-Binding Sites in Mn-Depleted Oxygen-Evolving Complexes of Photosystem II and on Fe Replacement of Mn in Mn-Containing, Ca-Depleted Complexes

Fe(II) cations bind with high efficiency and specificity at the high-affinity (HA), Mn-binding site (termed the “blocking effect” since Fe blocks further electron donation to the site) of the oxygen-evolving complex (OEC) in Mn-depleted, photosystem II (PSII) membrane fragments (Semin et al. in Biochemistry 41:5854, 2002). Furthermore, Fe(II) cations can substitute for 1 or 2Mn cations (pH dependent) in Ca-depleted PSII membranes (Semin et al. in Journal of Bioenergetics and Biomembranes 48:227, 2016; Semin et al. in Journal of Photochemistry and Photobiology B 178:192, 2018). In the current study, we examined the effect of Ca2+ cations on the interaction of Fe(II) ions with Mn-depleted [PSII(-Mn)] and Ca-depleted [PSII(-Ca)] photosystem II membranes. We found that Ca2+ cations (about 50 mM) inhibit the light-dependent oxidation of Fe(II) (5 µM) by about 25% in PSII(-Mn) membranes, whereas inhibition of the blocking process is greater at about 40%. Blocking of the HA site by Fe cations also decreases the rate of charge recombination between QA- and YZ•+ from t1/2?=?30 ms to 46 ms. However, Ca2+ does not affect the rate during the blocking process. An Fe(II) cation (20 µM) replaces 1Mn cation in the Mn4CaO5 catalytic cluster of PSII(-Ca) membranes at pH 5.7 but 2 Mn cations at pH 6.5. In the presence of Ca2+ (10 mM) during the substitution process, Fe(II) is not able to extract Mn at pH 5.7 and extracts only 1Mn at pH 6.5 (instead of two without Ca2+). Measurements of fluorescence induction kinetics support these observations. Inhibition of Mn substitution with Fe(II) cations in the OEC only occurs with Ca2+ and Sr2+ cations, which are also able to restore oxygen evolution in PSII(-Ca) samples. Nonactive cations like La3+, Ni2+, Cd2+, and Mg2+ have no influence on the replacement of Mn with Fe. These results show that the location and/or ligand composition of one Mn cation in the Mn4CaO5 cluster is strongly affected by calcium depletion or rebinding and that bound calcium affects the redox potential of the extractable Mn4 cation in the OEC, making it resistant to reduction.

calcium↗
DOE OSTI2026

Adsorption-Engineered Hydrocarbon Ionomers for Durable Proton-Exchange Membrane Fuel Cells

Reducing reliance on perfluoroalkyl substances (PFAS) in proton-exchange membrane fuel cells requires hydrocarbon ionomers that combine high performance with long-term durability, a persistent challenge in catalyst-layer design. Here, we identify oxidation-driven ionomer-catalyst interfacial degradation as a dominant failure pathway in hydrocarbon ionomer-bonded cathodes and introduce an adsorption-engineering strategy to overcome this limitation. The comparison of a commercial sulfonated poly(phenylene) (Pemion) with structurally engineered sulfonated poly(fluorene)s demonstrated that electrode durability is governed by the interplay between ionomer adsorption strength and resistance to oxidative degradation on carbon-supported Pt catalysts. A poly(fluorene) ionomer with mobile alkyl sulfonic acid groups forms resilient interfaces, delivering 1.28 A cm−2 at 0.65 V under fully humidified H2/air conditions (80°C and 150 kPaabs), comparable to Pemion. After 90,000 accelerated potential cycles, the poly(fluorene)-bonded cathode exhibits significantly improved durability, with only 29% performance loss compared to 58% for Pemion; further molecular refinement reduces the loss to 17%, approaching that of Nafion-bonded cathodes (14%). These findings establish adsorption-engineered ionomer design that decouples interfacial anchoring from oxidative degradation as a general strategy for achieving durable, high-performance PFAS-free PEM fuel cell electrodes.

08 HYDROGEN↗
DOE OSTI2020

The membrane periodic skeleton is an actomyosin network that regulates axonal diameter and conduction

Neurons have a membrane periodic skeleton (MPS) composed of actin rings interconnected by spectrin. Here, combining chemical and genetic gain- and loss-of-function assays, we show that in rat hippocampal neurons the MPS is an actomyosin network that controls axonal expansion and contraction. Using super-resolution microscopy, we analyzed the localization of axonal non-muscle myosin II (NMII). We show that active NMII light chains are colocalized with actin rings and organized in a circular periodic manner throughout the axon shaft. In contrast, NMII heavy chains are mostly positioned along the longitudinal axonal axis, being able to crosslink adjacent rings. NMII filaments can play contractile or scaffolding roles determined by their position relative to actin rings and activation state. We also show that MPS destabilization through NMII inactivation affects axonal electrophysiology, increasing action potential conduction velocity. In summary, our findings open new perspectives on axon diameter regulation, with important implications in neuronal biology.

Costa, Ana Rita↗
DOE OSTI2020

Proton-conducting oxides for energy conversion and storage

Proton-conducting oxides are a class of solid-state ion-conducting ceramic materials that demonstrate significant hydrogen ion (proton) conductivity at intermediate temperatures (e.g., 300–700 °C). They are garnering significant attention due to several unique characteristics that distinguish them from both higher temperature oxygen ion conducting oxides and lower temperature proton-conducting polymers. By enabling proton-mediated electrochemistry under both dry and wet environments at moderate temperatures, protonic ceramics provide unique opportunities to enhance or synergize a diverse range of complementary electrochemical and thermochemical processes. Because of this potential, significant efforts have been devoted to advancing numerous energy-related applications using these materials. This review aims to comprehensively summarize these applications and analyze the most up-to-date and future developments of proton-conducting oxides. We aim to bring together this diverse subject matter by integrating the fundamentals of proton-conducting oxides with application-oriented insights. We begin with a historical roadmap, followed by a basic overview of the materials, theories and fundamentals, and fabrication and processing technologies underlying the field. The central section of our review summarizes major applications and developments of proton-conducting ceramics, ranging from maturing applications approaching commercialization to embryonic technologies just now emerging from the lab. These include protonic ceramic fuel cells, protonic ceramic electrolysis cells, reversible protonic ceramic electrochemical cells, protonic ceramic membrane reactors, and protonic ceramic electrochemical reactors. For each application, we analyze both the prospects and challenges and offer recommendations for future research directions so that tomorrow's researchers can continue to advance the development and commercialization of these fascinating materials.

Duan, Chuancheng (ORCID:0000000218261415)↗
DOE OSTI2026

Mitigating Hydrogen-Induced Degradation of Iridium Anodes in Proton Exchange Membrane Water Electrolyzers

One promising method for reducing precious metal usage in proton exchange membrane water electrolysis is lowering iridium (Ir) loading at the anode. However, low-loading Ir catalysts often suffer from poor stability under high current densities. In this study, hydrogen (H2) crossover from the cathode to the anode is identified as a key degradation pathway. Temperature-programmed reduction confirms the reduction of IrO2 at 80 °C in a hydrogen environment, highlighting the vulnerability of IrO2-based catalysts to H2 exposure. To mitigate this effect, palladium (Pd) is introduced as an anode additive, acting as an H2 oxidation catalyst and mitigating IrO2 reduction. This protective role is verified by inductively coupled plasma optical emission spectroscopy and in situ X-ray absorption spectroscopy, showing significantly suppressed Ir dissolution at 80 °C under H2 flow when an O-covered Pd surface is present at oxygen evolution reaction potentials. Results from the current study identify a new strategy in improving activity and durability of catalysts in electrolyzers.

58 GEOSCIENCES↗
DOE OSTI2023

Regulating Catalytic Properties and Thermal Stability of Pt and PtCo Intermetallic Fuel-Cell Catalysts via Strong Coupling Effects between Single-Metal Site-Rich Carbon and Pt

Developing low platinum-group-metal (PGM) catalysts for the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs) for heavy-duty vehicles (HDVs) remains a great challenge due to the highly demanded power density and long-term durability. Here, this work explores the possible synergistic effect between single Mn site-rich carbon (Mn SA -NC) and Pt nanoparticles, aiming to improve intrinsic activity and stability of PGM catalysts. Density functional theory (DFT) calculations predicted a strong coupling effect between Pt and MnN 4 sites in the carbon support, strengthening their interactions to immobilize Pt nanoparticles during the ORR. The adjacent MnN 4 sites weaken oxygen adsorption at Pt to enhance intrinsic activity. Well-dispersed Pt (2.1 nm) and ordered L1 2 -Pt 3 Co nanoparticles (3.3 nm) were retained on the Mn SA -NC support after indispensable high-temperature annealing up to 800 °C, suggesting enhanced thermal stability. Both PGM catalysts were thoroughly studied in membrane electrode assemblies (MEAs), showing compelling performance and durability. The Pt@Mn SA -NC catalyst achieved a mass activity (MA) of 0.63 A mg Pt –1 at 0.9 V iR-free and maintained 78% of its initial performance after a 30,000-cycle accelerated stress test (AST). The L1 2 -Pt 3 Co@Mn SA -NC catalyst accomplished a much higher MA of 0.91 A mg Pt –1 and a current density of 1.63 A cm –2 at 0.7 V under traditional light-duty vehicle (LDV) H 2 –air conditions (150 kPa abs and 0.10 mg Pt cm –2 ). Furthermore, the same catalyst in an HDV MEA (250 kPa abs and 0.20 mg Pt cm –2 ) delivered 1.75 A cm –2 at 0.7 V, only losing 18% performance after 90,000 cycles of the AST, demonstrating great potential to meet the DOE targets.

25 ENERGY STORAGE↗
DOE OSTI2020

Kinetics Modeling for Design of Continuous Enzymatic Hydrolysis

Enzymatic hydrolysis of cellulose to monomeric sugars continues to be a limiting step in cost-effectively producing sugar and fermentation-based biofuels from biomass. In particular, the high cost of enzymes coupled with the long time-scale of reaction pose challenges to economic viability. Performing enzymatic hydrolysis in a continuous mode with enzyme recycle may provide a path towards substantially reduced costs for sugar production, but design and analysis are complicated by a lack of suitable kinetics models. Computationally attainable models, such as fractal-based models, require knowledge of the reaction-history of the biomass, and are thus only suitable for describing the batch reactions from which they are derived. Fundamental models, while potentially more generalizable, are often too computationally intensive to use in process or reactor modeling. In this work, a phenomenological rate model is proposed based on a two-phase substrate representation. Good agreement is seen between batch and continuous enzymatic hydrolysis (CEH) experiment data, which validates the model and enables us to solve for reactor design parameters, such as CEH reactor size and stream flow rates, based on process variables like yield. This model is integrated with techno-economic analysis software to explore economic sensitivities. Important design optimizations and tradeoffs are identified and quantified, including the relative cost imposed by rate slowdown from sugar inhibition versus the cost to remove and concentrate sugars at a lower concentration. It also identifies, high-leverage avenues for further exploration, such as increasing the maximum feasible solids concentration, and sustaining high membrane flux and reliability.

09 BIOMASS FUELS↗
DOE OSTI2025

Complexing Agent-Assisted Membraneless Zinc–Iodine Aqueous Batteries

A membrane is required for conventional zinc–iodine aqueous batteries, since soluble polyiodides cross over to the anode side and react with zinc metal spontaneously. Making the battery membraneless increases ion transport and reduces its cost and overall footprint. In this paper, a membraneless Zn–I 2 aqueous battery is demonstrated, employing a complexing agent, 1-butyl-1-methylpyrrolidinium iodide (MBPI), to promote the formation of I 5 – -containing, phase-separated polyiodides upon charging, to minimize self-discharge and suppress Zn dendrite growth. With an additional 0.3 M MBPI in 4 M ZnI 2 electrolyte, the membraneless battery achieved 65 cycles with >85% Coulombic efficiency, whereas the MBPI-free control failed immediately. Additionally, a volumetric capacity of 14.3 Ah L –1 was achieved, surpassing those of most membraneless batteries reported to date regardless of redox chemistry, and underscores the potential of complexing agents in simplifying the architecture of conventional Zn–I 2 flow batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

Evolution of eggshell structure in relation to nesting ecology in non-avian reptiles

Amniotic eggs are multifunctional structures that enabled early tetrapods to colonize the land millions of years ago, and are now the reproductive mode of over 70% of all terrestrial amniotes. Eggshell morphology is at the core of animal survival, mediating the interactions between embryos and their environment, and has evolved into a massive diversity of forms and functions in modern reptiles. These functions are critical to embryonic survival and may serve as models for new antimicrobial and/or breathable membranes. However, we still lack critical data on the basic structural and functional properties of eggs, particularly of reptiles. Here, we first characterized egg shape, shell thickness, porosity, and mineralization of eggs from 91 reptile species using optical images, scanning electron microscopy, and micro computed tomography, and collected data on nesting ecology from the literature. We then used comparative analyses to test hypotheses on the selective pressures driving their evolution. We hypothesized that eggshell morphology has evolved to protect shells from physical damage and desiccation, and, in support, found a positive relationship between thickness and precipitation, and a negative relationship between porosity and temperature. Although mineralization varied extensively, it was not correlated with nesting ecology variables. Ancestral state reconstructions show thinning and increased porosity over evolutionary time in squamates, but the opposite in turtles and crocodilians. Egg shape, size, porosity and calcification were correlated, suggesting potential structural or developmental tradeoffs. This study provides new data and insights into the morphology and evolution of reptile eggs, and raises numerous questions for additional research.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Dry electrodes with a printed cellulose–graphene ink for low-profile strain sensors in electromyography

Dihydrolevoglucosenone, commonly known as Cyrene, is a renewable and fully biodegradable cellulose-waste derived, environmentally friendly solvent, presenting a non-toxic alternative to N-methyl-2-pyrrolidone (NMP). Currently, solution-based processing of graphene and other similar van der Waals solids favor toxic solvents such as NMP, limiting their use for biosensing. However, with the use of Cyrene, bio-compatible printable devices are possible, and studies have already demonstrated its use in temperature and other biosensing methods through screen-printing. Screen-printing unfortunately often requires masks that constrain the minimum acquirable feature size to be above hundreds of centimeters and wastes material, adding to process complexity and cost. Conversely, inkjet-printing is an attractive alternative for the maskless patterning of hierarchically assembled structures, with micron length scales attainable. Graphene's high conductivity positions it ideally for long-wear sensors such as dry electrodes or respiration monitors. Here, we demonstrate the potential of Cyrene-based graphene inks through few-layer inkjet printing on flexible substrates for the first time, to produce non-toxic conductors toward a strain-mediated mechanism for biosensing, used to detect bodily motion for wearable electronics. The challenges overcome in this study include engineering ink chemistry and printing parameters such that Cyrene's relatively high viscosity compared to typical inkjet solvents, still allows for droplet ejection in a conventional material printer, yielding well-resolved clean line-edges in contrast to other solvents that exhibit diffuse line-edges possibly from stray droplets and ink-splashing. Temperature-dependent transport measurements on the inkjet-printed Cyrene-based graphene films showed the conductivity to be largely temperature-invariant but at lower temperatures below 100 K, conductivity decreased, likely as a result of increased inter-membrane separation arising from thermal contraction. Additionally, temperature-dependent Raman spectroscopy showed the red-shift in the G-band, 2D-band and D-band peaks, as temperature increased. As a result, by validating flexion motion detection of the proximal interphalangeal joint demonstrated in this study, our work is the first of its kind to successfully additively manufacture inkjet-printed Cyrene-based graphene strain sensors on flexible substrates for bio-sensing and wearables.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Periplasmic biomineralization for semi-artificial photosynthesis

Semiconductor-based biointerfaces are typically established either on the surface of the plasma membrane or within the cytoplasm. In Gram-negative bacteria, the periplasmic space, characterized by its confinement and the presence of numerous enzymes and peptidoglycans, offers additional opportunities for biomineralization, allowing for nongenetic modulation interfaces. We demonstrate semiconductor nanocluster precipitation containing single- and multiple-metal elements within the periplasm, as observed through various electron- and x-ray-based imaging techniques. The periplasmic semiconductors are metastable and display defect-dominant fluorescent properties. Unexpectedly, the defect-rich (i.e., the low-grade) semiconductor nanoclusters produced in situ can still increase adenosine triphosphate levels and malate production when coupled with photosensitization. We expand the sustainability levels of the biohybrid system to include reducing heavy metals at the primary level, building living bioreactors at the secondary level, and creating semi-artificial photosynthesis at the tertiary level. The biomineralization-enabled periplasmic biohybrids have the potential to serve as defect-tolerant platforms for diverse sustainable applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Genomic adaptations of the green alga Dunaliella salina to life under high salinity

Life in high salinity environments poses challenges to cells in a variety of ways: maintenance of ion homeostasis and nutrient acquisition, often while concomitantly enduring saturating irradiances. Dunaliella salina has an exceptional ability to thrive even in saturated brine solutions. This ability has made it a model organism for studying responses to abiotic stress factors. Here we describe the occurrence of unique gene families, expansion of gene families, or gene losses that might be linked to osmoadaptive strategies. We discovered multiple unique genes coding for several of the homologous superfamily of the Ser-Thr-rich glycosyl-phosphatidyl-inositol-anchored membrane family and of the glycolipid 2-alpha-mannosyltransferase family, suggesting that such components on the cell surface are essential to life in high salt. Gene expansion was found in families that participate in sensing of abiotic stress and signal transduction in plants. One example is the patched family of the Sonic Hedgehog receptor proteins, supporting a previous hypothesis that plasma membrane sterols are important for sensing changes in salinities in D. salina. We also investigated genome-based capabilities regarding glycerol metabolism and present an extensive map for core carbon metabolism. We postulate that a second broader glycerol cycle exists that also connects to photorespiration, thus extending the previously described glycerol cycle. Further genome-based analysis of isoprenoid and carotenoid metabolism revealed duplications of genes for 1-deoxy-D-xylulose-5-phosphate synthase (DXS) and phytoene synthase (PSY), with the second gene copy of each enzyme being clustered together. Moreover, we identified two genes predicted to code for a prokaryotic-type phytoene desaturase (CRTI), indicating that D. salina may have eukaryotic and prokaryotic elements comprising its carotenoid biosynthesis pathways. In brief, our genomic data provide the basis for further gene discoveries regarding sensing abiotic stress, the metabolism of this halophilic alga, and its potential in biotechnological applications.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Maximizing Marine Carbon Removal by Coupling Electrochemical and Biological Methods

Integrated development of emerging marine decarbonization strategies offers the possibility of lowering CO2 removal costs and enabling their widespread deployment. In this study we examine the feasibility and benefits of coupling electrochemical and biological marine carbon removal strategies. Bipolar membrane electrodialysis (BPMED) is used to generate acid and alkalinity from seawater and electricity, and the alkalinity is returned to the ocean for indirect CO2 removal from the atmosphere, but the acid stream is a waste product. Considering the large-scale of CO2 removal necessary, the acid storage, neutralization, and disposal have prohibitive costs and carbon footprint. Here we investigate the feasibility to valorize the acid stream to enhance the growth and CO2 uptake through photosynthesis in the fast-growing marine phytoplankter Picochlorum celeri. When added to active algae cultures, the BPMED-generated acidified seawater alters the carbonate-bicarbonate equilibrium thereby increasing the bioavailability of CO2 and the observed growth rates. Additions of up to 2 mM H+ from BPMED effluent streams increased algal productivity up to 3-fold. A high-level analysis conducted based on experimental data to estimate the potential of sequestered CO2 emissions when compared to conventional commercial means of acid utilization or disposal, is estimated to be ~30 kgCO2 / kgacid. Through further development and optimization in terms of choice of algal species, growth conditions, acid addition rates, etc. the combined electrochemical-biological approach has the potential to achieve higher net CO2 removal.

carbon dioxide, marine, marine algae↗
DOE OSTI2023

Fuel Cell Stack Model for Real-Time Simulation of Grid-Connected Applications

Fuel cell stacks coupled with electrolyzers and hydrogen storage sites can be a promising category of distributed energy resources for both grid-connected and stand-alone power systems. However, because of high costs, at-scale hardware testing of fuel cell stacks for grid-connected applications is not economically viable at present. A model-based system that can accurately captures the steady-state and dynamic response of fuel cell stacks over long time periods (hours), is needed. This paper demonstrate a real-time electromagnetic transient model of a megawatt-scale, grid-connected proton exchange membrane fuel cell stack, coupled with a mass-based hydrogen storage system. This model can emulate the electrical steady-state and dynamic response of grid-connected fuel cell stacks. We validate the model using the response of commercial hardware fuel cell stacks and analytical models in the literature - using a digital real-time simulator (RSCAD). The proposed real-time model is then used to simulate cases spanning different time horizons and to design controller-hardware-in-the-loop experiments to evaluate controllers for hydrogen stations.

activation potential↗
DOE OSTI2021

GLIDR promotes the progression of glioma by regulating the miR-4677-3p/MAGI2 axis

Gliomas are the most common and fatal primary brain tumors. Growing evidence suggests that long non-coding RNAs (lncRNAs) constitute novel and potential therapeutic targets for glioma. However, the biological role of glioblastoma down-regulated RNA (GLIDR) in glioma remains largely elusive. In the current study, we used quantitative real-time polymerase chain reaction (qRT-PCR) to detect GLIDR expression in glioma cells. Cell counting kit 8 (CCK-8) assay, colony formation assay, JC-1 staining, and flow cytometry were used to evaluate the role of GLIDR in proliferation and apoptosis of glioma cells. Western blotting was performed to assess the effect of GLIDR on the level of apoptosis-related proteins. In addition, bioinformatics prediction, RNA immunoprecipitation (RIP), RNA pull-down, and luciferase reporter gene assays were used to study the regulatory mechanisms of GLIDR in glioma. GLIDR was found to be highly expressed in glioma cells and silencing of GLIDR inhibited cell proliferation and promoted apoptosis. Functionally, GLIDR bound to miR-4677-3p that directly targeted membrane-associated guanylate kinase, WW, and PDZ domain-containing protein 2 (MAGI2). Our data showed that GLIDR affects the proliferation and apoptosis of glioma cells by targeting miR-4677-3p to regulate the expression of MAGI2. In conclusion, our study determined the oncogenic role of GLIDR in glioma, which may provide a new perspective for the treatment of glioma.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

The Impact of Catalyst Layer Composition and Structure on Performance and Durability of PEMWE Anodes

A study of various compositions of anodes for proton exchange membrane water electrolysis aimed at reducing precious metal content and system costs without compromising performance and durability is presented. A key challenge in current water electrolysis technologies is the reliance on high iridium loadings to ensure sufficient catalytic activity, electronic conductivity, and durability for the oxygen evolution reaction. To address this, catalyst layers based on the stable but kinetically limited rutile phase of iridium oxide are combined with platinum nanoparticles and carbon-based additives to improve structural properties and ink processability. By systematically varying the volume ratios of carbon to precious metals and ionomer to solids, compositional trends have been identified, and significant performance improvements have been achieved. Structural and elemental analysis confirms improved dispersion of platinum and iridium can be achieved, as well as electronic conductivity improvements within the catalyst layer. Polarization curve analysis has shown the ability of added Pt and C to significantly increase catalytic activity. These results highlight the potential positive impact of Pt and C on anode structure, composition, and cell performance.

36 MATERIALS SCIENCE↗
DOE OSTI2023

VPS26 Moonlights as an Arrestin-like Adapter for a 7-transmembrane RGS 2 protein in Arabidopsis thaliana

Extracellular signals perceived by 7-transmembrane (7TM)-spanning receptors on the plasma membrane utilize a cytoplasmic adaptor that propagates signaling and initiates a feedback circuit for desensitization by removal of these receptors at the plasma membrane leading to desensitization to that signal. Signal (agonist) binding often evokes phosphorylation at the C-terminal tail of many 7TM G-protein-coupled receptors in animal cells which then recruits a cytoplasmic intermediate adaptor, β-arrestin, that sets in motion clathrin-mediated endocytosis (CME). Some 7TM receptors have agonist-induced phosphorylation and CME that do not involve β-arrestin, therefore it is unclear how these phosphorylated 7TM receptors are internalized. Arrestins, neither α– or β-types, are not encoded in the Arabidopsis genome, yet Arabidopsis cells have a well characterized signal-induced CME of a 7TM protein, Regulator of G Signaling 1 (AtRGS1). We show that a component of the retromer complex, VPS26, moonlights as an arrestin-like adapter. VPS26A and VPS26B form heterodimer instead of homodimer or monomer. flg22, a bacterium-derived signal that alerts plant cells of the presence of a potential pathogen, induces phosphorylation of AtRGS1 within a cluster of serines in its C-terminal tail, dimerization, and its CME. The phosphorylated C-terminal tail peptide binds to VPS26A/B heterodimer with greater affinity than the unphosphorylated peptide. We propose that VPS26 serves as an arrestin-like adaptor in the CME of AtRGS1 dimerization biased for VPS26 signaling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗