Structural mechanism of ligand activation in human GABAB receptor

Yong Geng,     Martin Bush,     Lidia Mosyak,     Feng Wang     & Qing R. Fan

                                                                            

Abstract:

Human GABAB (γ-aminobutyric acid class B) receptor is a G-protein-coupled receptor central to inhibitory neurotransmission in the brain. It functions as an obligatory heterodimer of the subunits GBR1 and GBR2. Here we present the crystal structures of a heterodimeric complex between the extracellular domains of GBR1 and GBR2 in the apo, agonist-bound and antagonist-bound forms. The apo and antagonist-bound structures represent the resting state of the receptor; the agonist-bound complex corresponds to the active state. Both subunits adopt an open conformation at rest, and only GBR1 closes on agonist-induced receptor activation. The agonists and antagonists are anchored in the interdomain crevice of GBR1 by an overlapping set of residues. An antagonist confines GBR1 to the open conformation of the inactive state, whereas an agonist induces its domain closure for activation. Our data reveal a unique activation mechanism for GABAB receptor that involves the formation of a novel heterodimer interface between subunits.

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Keywords:ligand,human,GABAB reeptor,heterodimer

Targeting Plasmodium PI(4)K to eliminate malaria

Case W. McNamara,     Marcus C. S. Lee,     Chek Shik Lim,     Siau Hoi Lim,     Jason Roland,     Advait Nagle,     Oliver Simon,     Bryan K. S. Yeung,     Arnab K. Chatterjee,     Susan L. McCormack,     Micah J. Manary,     Anne-Marie Zeeman,     Koen J. Dechering,     T. R. Santha Kumar,     Philipp P. Henrich, Kerstin Gagaring,     Maureen Ibanez,     Nobutaka Kato,     Kelli L. Kuhen,     Christoph Fischli, Matthias Rottmann,     David M. Plouffe,     Badry Bursulaya,     Stephan Meister,     Lucia Rameh

                                                                                        

Abstract:

Achieving the goal of malaria elimination will depend on targeting Plasmodium pathways essential across all life stages. Here we identify a lipid kinase, phosphatidylinositol-4-OH kinase (PI(4)K), as the target of imidazopyrazines, a new antimalarial compound class that inhibits the intracellular development of multiple Plasmodium species at each stage of infection in the vertebrate host. Imidazopyrazines demonstrate potent preventive, therapeutic, and transmission-blocking activity in rodent malaria models, are active against blood-stage field isolates of the major human pathogens P. falciparum and P. vivax, and inhibit liver-stage hypnozoites in the simian parasite P. cynomolgi. We show that imidazopyrazines exert their effect through inhibitory interaction with the ATP-binding pocket of PI(4)K, altering the intracellular distribution of phosphatidylinositol-4-phosphate. Collectively, our data define PI(4)K as a key Plasmodium vulnerability, opening up new avenues of target-based discovery to identify drugs with an ideal activity profile for the prevention, treatment and elimination of malaria.

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Keywords:plasmodium,malaria,imidazopyrazine,hypnozoites,phosphotidylinositol-4-OH,kinase

Ultrafast endocytosis at mouse hippocampal synapses

Shigeki Watanabe,     Benjamin R. Rost,     Marcial Camacho-Pérez,     M. Wayne Davis,     Berit Söhl-Kielczynski,     Christian Rosenmund     & Erik M. Jorgensen

                                                                                             

Abstract:

To sustain neurotransmission, synaptic vesicles and their associated proteins must be recycled locally at synapses. Synaptic vesicles are thought to be regenerated approximately 20 s after fusion by the assembly of clathrin scaffolds or in approximately 1 s by the reversal of fusion pores via ‘kiss-and-run’ endocytosis. Here we use optogenetics to stimulate cultured hippocampal neurons with a single stimulus, rapidly freeze them after fixed intervals and examine the ultrastructure using electron microscopy—‘flash-and-freeze’ electron microscopy. Docked vesicles fuse and collapse into the membrane within 30 ms of the stimulus. Compensatory endocytosis occurs within 50 to 100 ms at sites flanking the active zone. Invagination is blocked by inhibition of actin polymerization, and scission is blocked by inhibiting dynamin. Because intact synaptic vesicles are not recovered, this form of recycling is not compatible with kiss-and-run endocytosis; moreover, it is 200-fold faster than clathrin-mediated endocytosis. It is likely that ‘ultrafast endocytosis’ is specialized to restore the surface area of the membrane rapidly.

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Keywords:endocytosis,mouse,hippocampal,optogenetics,dynamin

Ferromagnetism in suspensions of magnetic platelets in liquid crystal

Alenka Mertelj,     Darja Lisjak,     Miha Drofenik     & Martin Čopič

                                                                                 

Abstract:

More than four decades ago, Brochard and de Gennes proposed that colloidal suspensions of ferromagnetic particles in nematic (directionally ordered) liquid crystals could form macroscopic ferromagnetic phases at room temperature. The experimental realization of these predicted phases has hitherto proved elusive, with such systems showing enhanced paramagnetism but no spontaneous magnetization in the absence of an external magnetic field. Here we show that nanometre-sized ferromagnetic platelets suspended in a nematic liquid crystal can order ferromagnetically on quenching from the isotropic phase. Cooling in the absence of a magnetic field produces a polydomain sample exhibiting the two opposing states of magnetization, oriented parallel to the direction of nematic ordering. Cooling in the presence of a magnetic field yields a monodomain sample; magnetization can be switched by domain wall movement on reversal of the applied magnetic field. The ferromagnetic properties of this dipolar fluid are due to the interplay of the nematic elastic interaction (which depends critically on the shape of the particles) and the magnetic dipolar interaction. This ferromagnetic phase responds to very small magnetic fields and may find use in magneto-optic devices.

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Keywords:ferromagnetism,magnetic platelets,liquid crystal,hitherto,paramagnetism

D14–SCFD3-dependent degradation of D53 regulates strigolactone signalling

Feng Zhou,     Qibing Lin,     Lihong Zhu,     Yulong Ren,     Kunneng Zhou,     Nitzan Shabek,     Fuqing Wu,     Haibin Mao,     Wei Dong,     Lu Gan,     Weiwei Ma,     He Gao,     Jun Chen,     Chao Yang,     Dan Wang, Junjie Tan,     Xin Zhang,     Xiuping Guo,     Jiulin Wang,     Ling Jiang,     Xi Liu,     Weiqi Chen,     Jinfang Chu,     Cunyu Yan,     Kotomi Ueno     et al.

                                                                                           

Abstract:

Strigolactones (SLs), a newly discovered class of carotenoid-derived phytohormones, are essential for developmental processes that shape plant architecture and interactions with parasitic weeds and symbiotic arbuscular mycorrhizal fungi. Despite the rapid progress in elucidating the SL biosynthetic pathway, the perception and signalling mechanisms of SL remain poorly understood. Here we show that DWARF 53 (D53) acts as a repressor of SL signalling and that SLs induce its degradation. We find that the rice (Oryza sativa) d53 mutant, which produces an exaggerated number of tillers compared to wild-type plants, is caused by a gain-of-function mutation and is insensitive to exogenous SL treatment. The D53 gene product shares predicted features with the class I Clp ATPase proteins and can form a complex with the α/β hydrolase protein DWARF 14 (D14) and the F-box protein DWARF 3 (D3), two previously identified signalling components potentially responsible for SL perception. We demonstrate that, in a D14- and D3-dependent manner, SLs induce D53 degradation by the proteasome and abrogate its activity in promoting axillary bud outgrowth. Our combined genetic and biochemical data reveal that D53 acts as a repressor of the SL signalling pathway, whose hormone-induced degradation represents a key molecular link between SL perception and responses.

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Keywords:D53,strigolactone,arbuscular mycorrhizal,Clp ATPase

DWARF 53 acts as a repressor of strigolactone signalling in rice

Liang Jiang,     Xue Liu,     Guosheng Xiong,     Huihui Liu,     Fulu Chen,     Lei Wang,     Xiangbing Meng, Guifu Liu,     Hong Yu,     Yundong Yuan,     Wei Yi,     Lihua Zhao,     Honglei Ma,     Yuanzheng He, Zhongshan Wu,     Karsten Melcher,     Qian Qian,     H. Eric Xu,     Yonghong Wang     & Jiayang Li

                                                                                   

Abstract:

Strigolactones (SLs) are a group of newly identified plant hormones that control plant shoot branching. SL signalling requires the hormone-dependent interaction of DWARF 14 (D14), a probable candidate SL receptor, with DWARF 3 (D3), an F-box component of the Skp–Cullin–F-box (SCF) E3 ubiquitin ligase complex. Here we report the characterization of a dominant SL-insensitive rice (Oryza sativa) mutant dwarf 53 (d53) and the cloning of D53, which encodes a substrate of the SCFD3 ubiquitination complex and functions as a repressor of SL signalling. Treatments with GR24, a synthetic SL analogue, cause D53 degradation via the proteasome in a manner that requires D14 and the SCFD3 ubiquitin ligase, whereas the dominant form of D53 is resistant to SL-mediated degradation. Moreover, D53 can interact with transcriptional co-repressors known as TOPLESS-RELATED PROTEINS. Our results suggest a model of SL signalling that involves SL-dependent degradation of the D53 repressor mediated by the D14–D3 complex.

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Keywords:DWARF 53,strigolactone,rice,ubiquitination,SKP-cullin-F-box

Astrocytes mediate synapse elimination through MEGF10 and MERTK pathways

Won-Suk Chung,     Laura E. Clarke,     Gordon X. Wang,     Benjamin K. Stafford,     Alexander Sher, Chandrani Chakraborty,     Julia Joung,     Lynette C. Foo,     Andrew Thompson,     Chinfei Chen, Stephen J. Smith     & Ben A. Barres

                                                                                            

Abstract:

To achieve its precise neural connectivity, the developing mammalian nervous system undergoes extensive activity-dependent synapse remodelling. Recently, microglial cells have been shown to be responsible for a portion of synaptic pruning, but the remaining mechanisms remain unknown. Here we report a new role for astrocytes in actively engulfing central nervous system synapses. This process helps to mediate synapse elimination, requires the MEGF10 and MERTK phagocytic pathways, and is strongly dependent on neuronal activity. Developing mice deficient in both astrocyte pathways fail to refine their retinogeniculate connections normally and retain excess functional synapses. Finally, we show that in the adult mouse brain, astrocytes continuously engulf both excitatory and inhibitory synapses. These studies reveal a novel role for astrocytes in mediating synapse elimination in the developing and adult brain, identify MEGF10 and MERTK as critical proteins in the synapse remodelling underlying neural circuit refinement, and have important implications for understanding learning and memory as well as neurological disease processes

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Keywords:astrocytes,MEGF10,MERTK,retinogeniculate,phagocytic,

A molecular marker of artemisinin-resistant Plasmodium falciparum malaria

Frédéric Ariey,     Benoit Witkowski,     Chanaki Amaratunga,     Johann Beghain,     Anne-Claire Langlois,     Nimol Khim,     Saorin Kim,     Valentine Duru,     Christiane Bouchier,     Laurence Ma, Pharath Lim,     Rithea Leang,     Socheat Duong,     Sokunthea Sreng,     Seila Suon,     Char Meng Chuor,     Denis Mey Bout,     Sandie Ménard,     William O. Rogers,     Blaise Genton,     Thierry Fandeur,     Olivo Miotto,     Pascal Ringwald,     Jacques Le Bras,     Antoine Berry     et al.

                                                                                    

Abstract:

Plasmodium falciparum resistance to artemisinin derivatives in southeast Asia threatens malaria control and elimination activities worldwide. To monitor the spread of artemisinin resistance, a molecular marker is urgently needed. Here, using whole-genome sequencing of an artemisinin-resistant parasite line from Africa and clinical parasite isolates from Cambodia, we associate mutations in the PF3D7_1343700 kelch propeller domain (‘K13-propeller’) with artemisinin resistance in vitro and in vivo. Mutant K13-propeller alleles cluster in Cambodian provinces where resistance is prevalent, and the increasing frequency of a dominant mutant K13-propeller allele correlates with the recent spread of resistance in western Cambodia. Strong correlations between the presence of a mutant allele, in vitro parasite survival rates and in vivo parasite clearance rates indicate that K13-propeller mutations are important determinants of artemisinin resistance. K13-propeller polymorphism constitutes a useful molecular marker for large-scale surveillance efforts to contain artemisinin resistance in the Greater Mekong Subregion and prevent its global spread.

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Keywords:artemisinin,plasmodium falciparium,malaria,cambodian

The complete genome sequence of a Neanderthal from the Altai Mountains

Kay Prüfer,     Fernando Racimo,     Nick Patterson,     Flora Jay,     Sriram Sankararaman,     Susanna Sawyer,     Anja Heinze,     Gabriel Renaud,     Peter H. Sudmant,     Cesare de Filippo,     Heng Li, Swapan Mallick,     Michael Dannemann,     Qiaomei Fu,     Martin Kircher,     Martin Kuhlwilm, Michael Lachmann,     Matthias Meyer,     Matthias Ongyerth,     Michael Siebauer,     Christoph Theunert,     Arti Tandon,     Priya Moorjani,     Joseph Pickrell,     James C. Mullikin     et al.

                                                                                  

Abstract:

We present a high-quality genome sequence of a Neanderthal woman from Siberia. We show that her parents were related at the level of half-siblings and that mating among close relatives was common among her recent ancestors. We also sequenced the genome of a Neanderthal from the Caucasus to low coverage. An analysis of the relationships and population history of available archaic genomes and 25 present-day human genomes shows that several gene flow events occurred among Neanderthals, Denisovans and early modern humans, possibly including gene flow into Denisovans from an unknown archaic group. Thus, interbreeding, albeit of low magnitude, occurred among many hominin groups in the Late Pleistocene. In addition, the high-quality Neanderthal genome allows us to establish a definitive list of substitutions that became fixed in modern humans after their separation from the ancestors of Neanderthals and Denisovans.

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Keywords:genome sequence,altai mountains,denisovans,interbreeding

Structural basis for Ca2+ selectivity of a voltage-gated calcium channel

Lin Tang,     Tamer M. Gamal El-Din,     Jian Payandeh,     Gilbert Q. Martinez,     Teresa M. Heard, Todd Scheuer,     Ning Zheng     & William A. Catterall

                                                                                      

Abstract:

Voltage-gated calcium (CaV) channels catalyse rapid, highly selective influx of Ca2+ into cells despite a 70-fold higher extracellular concentration of Na+. How CaV channels solve this fundamental biophysical problem remains unclear. Here we report physiological and crystallographic analyses of a calcium selectivity filter constructed in the homotetrameric bacterial NaV channel NaVAb. Our results reveal interactions of hydrated Ca2+ with two high-affinity Ca2+-binding sites followed by a third lower-affinity site that would coordinate Ca2+ as it moves inward. At the selectivity filter entry, Site 1 is formed by four carboxyl side chains, which have a critical role in determining Ca2+ selectivity. Four carboxyls plus four backbone carbonyls form Site 2, which is targeted by the blocking cations Cd2+ and Mn2+, with single occupancy. The lower-affinity Site 3 is formed by four backbone carbonyls alone, which mediate exit into the central cavity. This pore architecture suggests a conduction pathway involving transitions between two main states with one or two hydrated Ca2+ ions bound in the selectivity filter and supports a ‘knock-off’ mechanism of ion permeation through a stepwise-binding process. The multi-ion selectivity filter of our CaVAb model establishes a structural framework for understanding the mechanisms of ion selectivity and conductance by vertebrate CaV channels.

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Keywords:ca2+,voltage,gated,calcium channel,carboxyls,cations

Spread in model climate sensitivity traced to atmospheric convective mixing

Steven C. Sherwood,     Sandrine Bony     & Jean-Louis Dufresne

                                                                                       

Abstract:

Equilibrium climate sensitivity refers to the ultimate change in global mean temperature in response to a change in external forcing. Despite decades of research attempting to narrow uncertainties, equilibrium climate sensitivity estimates from climate models still span roughly 1.5 to 5 degrees Celsius for a doubling of atmospheric carbon dioxide concentration, precluding accurate projections of future climate. The spread arises largely from differences in the feedback from low clouds, for reasons not yet understood. Here we show that differences in the simulated strength of convective mixing between the lower and middle tropical troposphere explain about half of the variance in climate sensitivity estimated by 43 climate models. The apparent mechanism is that such mixing dehydrates the low-cloud layer at a rate that increases as the climate warms, and this rate of increase depends on the initial mixing strength, linking the mixing to cloud feedback. The mixing inferred from observations appears to be sufficiently strong to imply a climate sensitivity of more than 3 degrees for a doubling of carbon dioxide. This is significantly higher than the currently accepted lower bound of 1.5 degrees, thereby constraining model projections towards relatively severe future warming.

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Keywords:equilibrium,carbondioxide,warming