The endoplasmic reticulum-mitochondria encounter structure (ERMES) is a protein complex that plays a tethering role in physically connecting ER and mitochondria membranes. The ERMES complex is composed of Mdm12, Mmm1, and Mdm34, which have a SMP domain in common, and Mdm10. Here, we report the crystal structure of S. cerevisiae Mdm12. The Mdm12 forms a dimeric SMP structure through domain swapping of the b1-strand comprising residues 1-7. Biochemical experiments reveal a phospholipidbinding site located along a hydrophobic channel of the Mdm12 structure and that Mdm12 might have a binding preference for glycerophospholipids harboring a positively charged head group. Strikingly, both full-length Mdm12 and Mdm12 truncated to exclude the disordered region (residues 74-114) display the same organization in the asymmetric unit, although they crystallize as a tetramer and hexamer, respectively. Taken together, these studies provide a novel understanding of the overall organization of SMP domains in the ERMES complex, indicating that Mdm12 interacts with Mdm34 through head-to-head contact, and with Mmm1 through tail-to-tail contact of SMP domains.

The endoplasmic reticulum (ER)-mitochondria encounter structure (ERMES) comprises mitochondrial distribution and morphology 12 (Mdm12), maintenance of mitochondrial morphology 1 (Mmm1), Mdm34, and Mdm10 and mediates physical membrane contact sites and nonvesicular lipid trafficking between the ER and mitochondria in yeast. Herein, we report two crystal structures of the synaptotagmin-like mitochondrial lipid-binding protein (SMP) domain of Mmm1 and the Mdm12-Mmm1 complex at 2.8 Å and 3.8 Å resolution, respectively. Mmm1 adopts a dimeric SMP structure augmented with two extra structural elements at the N and C termini that are involved in tight self-association and phospholipid coordination. Mmm1 binds two phospholipids inside the hydrophobic cavity, and the phosphate ion of the distal phospholipid is specifically recognized through extensive H-bonds. A positively charged concave surface on the SMP domain not only mediates ER membrane docking but also results in preferential binding to glycerophospholipids such as phosphatidylcholine (PC), phosphatidic acid (PA), phosphatidylglycerol (PG), and phosphatidylserine (PS), some of which are substrates for lipid-modifying enzymes in mitochondria. The Mdm12-Mmm1 structure reveals two Mdm12s binding to the SMP domains of the Mmm1 dimer in a pairwise head-to-tail manner. Direct association of Mmm1 and Mdm12 generates a 210-Å-long continuous hydrophobic tunnel that facilitates phospholipid transport. The Mdm12-Mmm1 complex binds all glycerophospholipids except for phosphatidylethanolamine (PE) in vitro.

fabrication of blue-emitting Cd-free QDs are still under development. [7-10] Above all, the charging of QDs is an obstacle for manufacturing QD-LEDs with good performance. [11] The simple mechanism of EL is that electrons and holes are formed by charge injection, and light is generated by the electron-hole pair recombination. Hence, it is essential to understand the charging process by mimicking EL processes. The complementary combination of spectroscopic technology and electrochemical control helps emulate EL and explain the charging process whether the charges occupy quantum states or trap states. Recently, there has been an increase in research to improve QD luminescence capabilities and charge extraction properties by performing electrochemical charging studies on QD films. [1,12,13] Li et al. [13] have shown that electron injection into the ground excitonic state of CdSe/CdS QDs leads to the bleaching of 1S 3/2 1S e transition because of 1S e state filling. Qin et al. [14] have investigated how the photoluminescence (PL) lifetime changes in CdSeS/ZnS QD under electrochemical control with blinking dynamics. Gooding et al. [15] have studied the effects of hole and electron injection on the PL of CdSe/ CdS/ZnS QDs. Many studies have revealed the effect of electron injection on the optical properties in Cd-based QDs, which leads to environmental issues. Environmentally friendly III-V semiconductors, especially InP QDs, have recently emerged as the best alternative to toxic II-VI semiconductors. [16-17] Meanwhile, the surfaces of InP core QDs are easily oxidized when they are exposed to oxygen environments. As a countermeasure, overcoating nanocrystals with wider band-gap materials has proven to be the best option to increase stability against photo-oxidation and to enhance the photoluminescence quantum yield (PL QY). [5,18,19] For example, the inorganic core can be surrounded by the shell, such as ZnSe and ZnS. [20] Möbius et al. reported that the electrical charges generated by application of a mechanical load are injected into the QDs, leading to PL quenching in InP/ZnS-based device. [17] However, the spectroelectrochemical properties were not yet reported in InP QDs to the best of our knowledge. Recently, we have reported highly luminescent InP/ZnSe/ZnS QDs synthesized with as much high efficiency as state-of-the-art Cd-based QDs. [21] In this study, we analyze the spectroelectrochemical properties depending on mid-shell thickness to identify the effect of charging on highly luminescent InP Semiconductor quantum dots (QDs) are spotlighted as a key type of emissive material for the next generation of light-emitting diodes (LEDs). This work presents the investigation of the electrochemical charging effect on the absorption and emission of the InP/ZnSe/ZnS QDs with different mid-shell thicknesses. The excitonic peak is gradually bleached during electrochemical charging, which is caused by 1S e (or 1S h) state filling when the electron (or hole) is injected into the InP core. Additional charges also lead to photo...

Formation of the nucleus-vacuole junction (NVJ) is mediated by direct interaction between the vacuolar protein Vac8p and the outer nuclear endoplasmic reticulum membrane protein Nvj1p. Herein we report the crystal structure of Vac8p bound to Nvj1p at 2.4-Å resolution. Vac8p comprises a flexibly connected N-terminal H1 helix followed by 12 armadillo repeats (ARMs) that form a right-handed superhelical structure. The extended 80-Å-long loop of Nvj1p specifically binds the highly conserved inner groove formed from ARM1−12 of Vac8p. Disruption of the Nvj1p-Vac8p interaction results in the loss of tight NVJs, which impairs piecemeal microautophagy of the nucleus in Saccharomyces cerevisiae. Vac8p cationic triad (Arg276, Arg317, and Arg359) motifs interacting with Nvj1p are also critical to the recognition of Atg13p, a key component of the cytoplasm-to-vacuole targeting (CVT) pathway, indicating competitive binding to Vac8p. Indeed, mutation of the cationic triad abolishes CVT of Ape1p in vivo. Combined with biochemical data, the crystal structure reveals a Vac8p homodimer formed from ARM1, and this self-association, likely regulated by the flexible H1 helix and the C terminus of Nvj1p, is critical for Vac8p cellular functions. M embrane contact sites (MCSs) between subcellular compartments play pivotal roles in cellular processes such as cooperative lipid biosynthesis, ion homeostasis, and interorganellar trafficking of molecules in eukaryotic cells (1-3). MCSs are physically formed through dynamic and direct interactions between proteins that are located in two distinct subcompartments. The nucleus-vacuole junction (NVJ), one of the best-characterized MCSs, is a physical contact site between perinuclear and vacuolar membranes and mediates essential cellular processes such as piecemeal microautophagy of the nucleus (PMN) and lipid biosynthesis in yeast (4, 5). PMN is a selective autophagic recycling process stimulated by carbon or nitrogen starvation through the target of rapamycin signaling pathway in Saccharomyces cerevisiae. Upon nutrient starvation, the region of the nucleus in the vicinity of NVJs invaginates into the vacuolar lumen and forms a bleb-like structure, which is released as a vesicle and eventually degraded by vacuolar hydrolases (5, 6). Because PMN occurs at the NVJ sites, their formation is essential for the initiation of the PMN process (7). NVJs are also involved in lipid metabolism by recruiting the two lipid-modifying enzymes, oxystereol-binding proteins homology (Osh1p) involved in nonvesicular lipid trafficking and the enoyl-CoA reductase Tsc13p that mediates the synthesis of verylong-chain fatty acids (8-11).Previous studies revealed that NVJs are generated by forming tight interactions between Vac8p, a vacuolar membrane protein, and Nvj1p, a nuclear membrane protein (12). Vac8p was initially found as a key player in vacuole inheritance by cooperating with Vac17p, actin, profilin, and Myo2p (13). In addition, Vac8p has a crucial role in mediating the processing of aminopeptidase I through in...

EXD2 (3′-5′ exonuclease domain-containing protein 2) is an essential protein with a conserved DEDDy superfamily 3′-5′ exonuclease domain. Recent research suggests that EXD2 has two potential functions: as a component of the DNA double-strand break repair machinery and as a ribonuclease for the regulation of mitochondrial translation. Herein, electron microscope imaging analysis and proximity labeling revealed that EXD2 is anchored to the mitochondrial outer membrane through a conserved N-terminal transmembrane domain, while the C-terminal region is cytosolic. Crystal structures of the exonuclease domain in complex with Mn2+/Mg2+ revealed a domain-swapped dimer in which the central α5−α7 helices are mutually crossed over, resulting in chimeric active sites. Additionally, the C-terminal segments absent in other DnaQ family exonucleases enclose the central chimeric active sites. Combined structural and biochemical analyses demonstrated that the unusual dimeric organization stabilizes the active site, facilitates discrimination between DNA and RNA substrates based on divalent cation coordination and generates a positively charged groove that binds substrates.

We introduce UnaG as a green-to-dark photoswitching fluorescent protein capable of highquality super-resolution imaging with photon numbers equivalent to the brightest photoswitchable red protein. UnaG only fluoresces upon binding of a fluorogenic metabolite, bilirubin, enabling UV-free reversible photoswitching with easily controllable kinetics and low background under Epi illumination. The on-and off-switching rates are controlled by the concentration of the ligand and the excitation light intensity, respectively, where the dissolved oxygen also promotes the off-switching. The photo-oxidation reaction mechanism of bilirubin in UnaG suggests that the lack of ligand-protein covalent bond allows the oxidized ligand to detach from the protein, emptying the binding cavity for rebinding to a fresh ligand molecule. We demonstrate super-resolution single-molecule localization imaging of various subcellular structures genetically encoded with UnaG, which enables facile labeling and simultaneous multicolor imaging of live cells. UnaG has the promise of becoming a default protein for highperformance super-resolution imaging.

The main issue in developing a quantum dot light-emitting diode (QLED) display lies in successfully replacing heavy metals with environmentally benign materials while maintaining high-quality device performance. Nonradiative Auger recombination is one of the major limiting factors of QLED performance and should ideally be suppressed. This study scrutinizes the effects of the shell structure and composition on photoluminescence (PL) properties of InP/ZnSeS/ZnS quantum dots (QDs) through ensemble and single-dot spectroscopic analyses. Employing gradient shells is discovered to suppress Auger recombination to a high degree, allowing charged QDs to be luminescent comparatively with neutral QDs. The “lifetime blinking” phenomenon is observed as evidence of suppressed Auger recombination. Furthermore, single-QD measurements reveal that gradient shells in QDs reduce spectral diffusion and elevate the energy barrier for charge trapping. Shell composition dependency in the gradience effect is observed. An increase in the ZnS composition (ZnS >50%) in the gradient shell introduces lattice mismatch between the core and the shell and therefore rather reverses the effect and reduces the QD performance.

Artificial photonic synapses with morphologically controlled photoreception, allowing for area-dependent tunable light reception as well as information storage and learning, have potential for application in emerging photointeractive neuro-computing technologies. Herein, an artificially intelligent (AI) photonic synapse with area-density-tunable perovskite nano-cone arrays templated in a self-assembled block copolymer (BCP) is presented, which is based on a field effect transistor with a floating gate of photoreceptive perovskite crystal arrays preferentially synthesized in a micro-phase-segregated BCP film. These arrays are capable of electric charge (de)trapping and photoexcited charge generation, and they exhibit versatile synaptic functions of the nervous system, including paired-pulse facilitation and long-term potentiation, with excellent reliability. The area-density variable perovskite floating gate developed by off-centered spin coating process allows for emulating the human retina with a position-dependent spatial distribution of cones. 60 × 12 arrays of the developed synapse devices exhibit position-dependent dual functions of receptor and synapse. They are AI and exhibit a pattern recognition accuracy up to ≈90% when examined using the Modified National Institute of Standards and Technology handwritten digit pattern recognition test.