Mesoscopic quantum emitters from deterministic aggregates of conjugated polymers
Thomas Stangl, Philipp Wilhelm, Klaas Remmerssen, Sigurd Höger, Jan Vogelsang, and John M. Lupton
Bright and stable single-photon sources, based on molecular objects, have contributed to exploring the foundations of quantum mechanics and measurement theory. Because the photon emission rate scales with molecular size, the most direct approach to increasing brightness is to enlarge the molecular object itself. But how big can it become while still retaining molecular characteristics of a deterministic photon source? We tackle this question by growing defined aggregates out of single chains of a conjugated polymer. Multichain aggregates show discrete single-photon emission, even when the individual chains display multiphoton emission. Single-aggregate spectroscopy reveals how coherent and incoherent excitonic intermolecular coupling mechanisms, known from the bulk, evolve with aggregate size. (See pp. E5560–E5566.)
Local and global structural drivers for the photoactivation of the orange carotenoid protein
Sayan Gupta, Miklos Guttman, Ryan L. Leverenz, Kulyash Zhumadilova, Emily G. Pawlowski, Christopher J. Petzold, Kelly K. Lee, Corie Y. Ralston, and Cheryl A. Kerfeld
The orange carotenoid protein (OCP) is critical for the antenna-associated energy-dissipation mechanism of cyanobacteria under high light conditions. We show that light activation causes a global conformation change, the complete separation of the two domains of the OCP. Such a conformational change has been postulated to be a prerequisite for interaction with the antenna. We also identify local structural changes in residue solvent accessibility and roles for structural water molecules in activation of the OCP. By combining small-angle scattering, hydrogen-deuterium exchange, and X-ray hydroxyl radical footprinting studies, we were able to construct a model of the structural changes during the activation of the OCP with an unprecedented level of detail. (See pp. E5567–E5574.)
NhaA antiporter functions using 10 helices, and an additional 2 contribute to assembly/stability
Etana Padan, Tsafi Danieli, Yael Keren, Dudu Alkoby, Gal Masrati, Turkan Haliloglu, Nir Ben-Tal, and Abraham Rimon
The principal Na+/H+ antiporter of Escherichia coli (Ec-NhaA) is the best-characterized of the pH-regulated Na+/H+ exchangers that control cellular Na+ and H+ homeostasis, and the human homologues are potentially important drug targets. Identification of the essential components of NhaA is vital to understanding the function of the protein and has implications for evolution and protein design. Ec-NhaA has 12 helices, 2 of which (VI and VII) are absent from the growing number of secondary transporters that share the unique Ec-NhaA structural fold. Mutants deleted of helices VI and VII, which form an α-hairpin at the dimer interface, are defective in the assembly/stability of the Ec-NhaA dimer but retain significant transport activity, as well as regulatory properties. (See pp. E5575–E5582.)
Regulation of outer kinetochore Ndc80 complex-based microtubule attachments by the central kinetochore Mis12/MIND complex
Emily M. Kudalkar, Emily A. Scarborough, Neil T. Umbreit, Alex Zelter, Daniel R. Gestaut, Michael Riffle, Richard S. Johnson, Michael J. MacCoss, Charles L. Asbury, and Trisha N. Davis
During cell division, multisubunit kinetochores partition chromosomes while maintaining a grip on dynamic microtubules under tension. Previous work in Caenorhabditis elegans showed that the central kinetochore component, Mis12/MIND (Mtw1, Nsl1, Nnf1, Dsn1) complex, increases microtubule binding of outer kinetochore complexes, but the mechanism for this enhancement remains unknown. Here, we identify new contacts between MIND and the outer kinetochore Ndc80 (Ndc80, Nuf2, Spc24, Spc25) complex that are essential for interaction in vitro and for cell viability. Using single-molecule microscopy, we demonstrate that a single MIND complex enhances the microtubule binding of a single Ndc80 complex. Our results suggest a molecular mechanism for enhancing kinetochore–microtubule attachment by a central kinetochore component. (See pp. E5583–E5589.)
Motifs of VDAC2 required for mitochondrial Bak import and tBid-induced apoptosis
Shamim Naghdi, Péter Várnai, and György Hajnóczky
Voltage-dependent anion channel 2 (VDAC2), like other VDAC proteins, transports solutes across the outer mitochondrial membrane, but it is the only isoform that supports mitochondrial import of cell death-executing proteins, Bak/Bax. To address the underlying mechanism, we created chimeras of VDAC2 and VDAC1 and tested their competency to rescue Bak insertion and apoptosis in VDAC2-deficient cells. Our gain-of-function studies revealed that the middle domain (123–179 aa) is required for rescue. Loss-of-function studies identified two critical residues (T168, D170). Finally, applying these clues to recently solved structures we identified a discrete site on the cytoplasmic side of VDAC2's pore that likely supports Bak insertion and apoptosis. (See pp. E5590–E5599.)
Low load for disruptive mutations in autism genes and their biased transmission
Ivan Iossifov, Dan Levy, Jeremy Allen, Kenny Ye, Michael Ronemus, Yoon-ha Lee, Boris Yamrom, and Michael Wigler
Gene targets of de novo mutation in autistic children have a lighter load of rare disruptive variation than typical human genes. This finding suggests such mutations are under negative selection and autism genes are highly vulnerable to mutation. Disruptive variants in these genes have biased transmission: They are more frequently transmitted to affected children, and more often from mothers than from fathers. Targets of mutation in lower intelligence quotient (IQ) affected children have a lower load of disruptive mutations than targets of mutation in higher IQ affected children. Biased transmission is seen more frequently to affected children of lower IQ. These observations are consistent with a correlation between severity of mutations and phenotype, and based on them, we list candidate autism genes ordered by likelihood. (See pp. E5600–E5607.)
Regulation of calreticulin–major histocompatibility complex (MHC) class I interactions by ATP
Sanjeeva Joseph Wijeyesakere, Jessica K. Gagnon, Karunesh Arora, Charles L. Brooks III, and Malini Raghavan
Calreticulin mutants that disrupt ATP binding are shown to prolong cellular MHC class I interactions with calreticulin and with the transporter associated with antigen processing (TAP). To our knowledge, no previous studies have implicated a role for endoplasmic reticulum (ER) luminal ATP as a determinant of MHC class I assembly complex dynamics. These studies also reveal a role for the ATP–calreticulin interaction in broadly regulating the binding of calreticulin to cellular substrates. Because a large number of cell surface and secreted glycoproteins are calreticulin/calnexin substrates, these studies have broad significance toward understanding the cellular mechanisms of protein quality control. (See pp. E5608–E5617.)
STIM1–Ca2+ signaling modulates automaticity of the mouse sinoatrial node
Hengtao Zhang, Albert Y. Sun, Jong J. Kim, Victoria Graham, Elizabeth A. Finch, Igor Nepliouev, Guiling Zhao, Tianyu Li, W. J. Lederer, Jonathan A. Stiber, Geoffrey S. Pitt, Nenad Bursac, and Paul B. Rosenberg
Each heartbeat originates in the sinoatrial node (SAN), a collection of specialized cardiomyocytes (SANCs), which exhibit rhythmic action potentials and spontaneous Ca2+ transients. We have found that the Ca2+ sensor protein stromal interaction molecule 1 (STIM1) is enriched in the SANCs. Here we show that STIM1 Ca2+ signaling is important in SANCs to maintain the Ca2+ content of intracellular Ca2+ stores and that this contributes to maintaining the regular sinus rhythm of the heart. (See pp. E5618–E5627.)
Ubiquitin systems mark pathogen-containing vacuoles as targets for host defense by guanylate binding proteins
Arun K. Haldar, Clémence Foltz, Ryan Finethy, Anthony S. Piro, Eric M. Feeley, Danielle M. Pilla-Moffett, Masaki Komatsu, Eva-Maria Frickel, and Jörn Coers
The innate immune system protects the host against infections with a diverse set of microbes that include intracellular bacterial and protozoan pathogens residing within pathogen-containing vacuoles (PVs). Because PVs provide an intracellular niche permissive for microbial growth, their destruction is critical for host defense. In mammals, PV destruction is dependent on immunity-related GTPases and guanylate binding proteins (GBPs). Although it has been shown that GBPs translocate to and eliminate PVs, the mechanisms by which GBPs specifically bind to PVs were unknown. Here, we describe an immune pathway that results in the decoration of PVs with a small protein called ubiquitin. Ubiquitin-decorated PVs are subsequently recognized by GBPs, resulting in the elimination of PVs and their microbial inhabitants. (See pp. E5628–E5637.)
Placebo analgesia and its opioidergic regulation suggest that empathy for pain is grounded in self pain
Markus Rütgen, Eva-Maria Seidel, Giorgia Silani, Igor Riečanský, Allan Hummer, Christian Windischberger, Predrag Petrovic, and Claus Lamm
Empathy is of major importance for everyday social interaction. Recent neuroscientific models suggest that pain empathy relies on the activation of brain areas that are also engaged during the first-hand experience of pain. These models rely on rather unspecific and correlational evidence. Here, we show that inducing pain analgesia also reduces pain empathy, and that this is associated with decreased activation of empathy-related brain areas. We then document that blocking placebo analgesia via an opioid antagonist also blocks placebo analgesia effects on pain empathy. This finding suggests that pain empathy is grounded in neural responses and neurotransmitter activity related to first-hand pain. (See pp. E5638–E5646.)
Topology-defined units in numerosity perception
Lixia He, Ke Zhou, Tiangang Zhou, Sheng He, and Lin Chen
What is a number? The answer to this age-old and fundamental question of philosophy has increasingly benefited from recent scientific investigation using psychology and neuroscience. To verify the invariant nature of numerosity perception, we manipulated the numbers of items connected/enclosed in arbitrary and irregular forms while controlling for various low-level visual features in different tasks and across small and large numbers. Results were consistent with the topological account, namely that numbers were strongly influenced by topological invariants (connectivity and the inside/outside relationship): connecting/enclosing items led to robust numerosity underestimation, with the extent of underestimation increasing monotonically with the number of connected/enclosed items. Brain image results also provided evidence that numbers represented in the intraparietal sulcus were influenced by topology. (See pp. E5647–E5655.)