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Structure of nevanimibe-bound tetrameric human ACAT1 期刊论文
NATURE, 2020, 581 (7808) : 339-U214
作者:  Ma, Xiyu;  Claus, Lucas A. N.;  Leslie, Michelle E.;  Tao, Kai;  Wu, Zhiping;  Liu, Jun;  Yu, Xiao;  Li, Bo;  Zhou, Jinggeng;  Savatin, Daniel V.;  Peng, Junmin;  Tyler, Brett M.;  Heese, Antje;  Russinova, Eugenia;  He, Ping;  Shan, Libo
收藏  |  浏览/下载:52/0  |  提交时间:2020/07/03

The structure of human ACAT1 in complex with the inhibitor nevanimibe is resolved by cryo-electron microscopy.


Cholesterol is an essential component of mammalian cell membranes, constituting up to 50% of plasma membrane lipids. By contrast, it accounts for only 5% of lipids in the endoplasmic reticulum (ER)(1). The ER enzyme sterol O-acyltransferase 1 (also named acyl-coenzyme A:cholesterol acyltransferase, ACAT1) transfers a long-chain fatty acid to cholesterol to form cholesteryl esters that coalesce into cytosolic lipid droplets. Under conditions of cholesterol overload, ACAT1 maintains the low cholesterol concentration of the ER and thereby has an essential role in cholesterol homeostasis(2,3). ACAT1 has also been implicated in Alzheimer'  s disease(4), atherosclerosis(5) and cancers(6). Here we report a cryo-electron microscopy structure of human ACAT1 in complex with nevanimibe(7), an inhibitor that is in clinical trials for the treatment of congenital adrenal hyperplasia. The ACAT1 holoenzyme is a tetramer that consists of two homodimers. Each monomer contains nine transmembrane helices (TMs), six of which (TM4-TM9) form a cavity that accommodates nevanimibe and an endogenous acyl-coenzyme A. This cavity also contains a histidine that has previously been identified as essential for catalytic activity(8). Our structural data and biochemical analyses provide a physical model to explain the process of cholesterol esterification, as well as details of the interaction between nevanimibe and ACAT1, which may help to accelerate the development of ACAT1 inhibitors to treat related diseases.


  
Structural transitions in influenza haemagglutinin at membrane fusion pH 期刊论文
NATURE, 2020, 583 (7814) : 150-+
作者:  Wei, Kevin;  Korsunsky, Ilya;  Marshall, Jennifer L.;  Gao, Anqi;  Watts, Gerald F. M.;  Major, Triin;  Croft, Adam P.;  Watts, Jordan;  Blazar, Philip E.;  Lange, Jeffrey K.;  Thornhill, Thomas S.;  Filer, Andrew;  Raza, Karim;  Donlin, Laura T.;  Siebel, Christian W.
收藏  |  浏览/下载:36/0  |  提交时间:2020/07/03

Cryo-electron microscopy studies of the influenza haemagglutinin glycoprotein at the low pH of host endosomes reveals structural intermediates, offering a dynamic view of how the protein mediates membrane fusion.


Infection by enveloped viruses involves fusion of their lipid envelopes with cellular membranes to release the viral genome into cells. For HIV, Ebola, influenza and numerous other viruses, envelope glycoproteins bind the infecting virion to cell-surface receptors and mediate membrane fusion. In the case of influenza, the receptor-binding glycoprotein is the haemagglutinin (HA), and following receptor-mediated uptake of the bound virus by endocytosis(1), it is the HA that mediates fusion of the virus envelope with the membrane of the endosome(2). Each subunit of the trimeric HA consists of two disulfide-linked polypeptides, HA1 and HA2. The larger, virus-membrane-distal, HA1 mediates receptor binding  the smaller, membrane-proximal, HA2 anchors HA in the envelope and contains the fusion peptide, a region that is directly involved in membrane interaction(3). The low pH of endosomes activates fusion by facilitating irreversible conformational changes in the glycoprotein. The structures of the initial HA at neutral pH and the final HA at fusion pH have been investigated by electron microscopy(4,5) and X-ray crystallography(6-8). Here, to further study the process of fusion, we incubate HA for different times at pH 5.0 and directly image structural changes using single-particle cryo-electron microscopy. We describe three distinct, previously undescribed forms of HA, most notably a 150 angstrom-long triple-helical coil of HA2, which may bridge between the viral and endosomal membranes. Comparison of these structures reveals concerted conformational rearrangements through which the HA mediates membrane fusion.


  
Electromechanical coupling in the hyperpolarization-activated K+ channel KAT1 期刊论文
NATURE, 2020, 583 (7814) : 145-+
作者:  Jin, Zhenming;  Du, Xiaoyu;  Xu, Yechun;  Deng, Yongqiang;  Liu, Meiqin;  Zhao, Yao;  Zhang, Bing;  Li, Xiaofeng;  Zhang, Leike;  Peng, Chao;  Duan, Yinkai;  Yu, Jing;  Wang, Lin;  Yang, Kailin;  Liu, Fengjiang;  Jiang, Rendi;  Yang, Xinglou;  You, Tian;  Liu, Xiaoce
收藏  |  浏览/下载:56/0  |  提交时间:2020/07/03

Voltage-gated potassium (K-v) channels coordinate electrical signalling and control cell volume by gating in response to membrane depolarization or hyperpolarization. However, although voltage-sensing domains transduce transmembrane electric field changes by a common mechanism involving the outward or inward translocation of gating charges(1-3), the general determinants of channel gating polarity remain poorly understood(4). Here we suggest a molecular mechanism for electromechanical coupling and gating polarity in non-domain-swapped K-v channels on the basis of the cryo-electron microscopy structure of KAT1, the hyperpolarization-activated K-v channel from Arabidopsis thaliana. KAT1 displays a depolarized voltage sensor, which interacts with a closed pore domain directly via two interfaces and indirectly via an intercalated phospholipid. Functional evaluation of KAT1 structure-guided mutants at the sensor-pore interfaces suggests a mechanism in which direct interaction between the sensor and the C-linker hairpin in the adjacent pore subunit is the primary determinant of gating polarity. We suggest that an inward motion of the S4 sensor helix of approximately 5-7 angstrom can underlie a direct-coupling mechanism, driving a conformational reorientation of the C-linker and ultimately opening the activation gate formed by the S6 intracellular bundle. This direct-coupling mechanism contrasts with allosteric mechanisms proposed for hyperpolarization-activated cyclic nucleotide-gated channels(5), and may represent an unexpected link between depolarization- and hyperpolarization-activated channels.


The cryo-electron microscopy structure of the hyperpolarization-activated K+ channel KAT1 points to a direct-coupling mechanism between S4 movement and the reorientation of the C-linker.


  
A lower X-gate in TASK channels traps inhibitors within the vestibule 期刊论文
NATURE, 2020
作者:  Chen, Tao;  Nomura, Kinya;  Wang, Xiaolin;  Sohrabi, Reza;  Xu, Jin;  Yao, Lingya;  Paasch, Bradley C.;  Ma, Li;  Kremer, James;  Cheng, Yuti;  Zhang, Li;  Wang, Nian;  Wang, Ertao;  Xin, Xiu-Fang;  He, Sheng Yang
收藏  |  浏览/下载:64/0  |  提交时间:2020/07/03

TWIK-related acid-sensitive potassium (TASK) channels-members of the two pore domain potassium (K-2P) channel family-are found in neurons(1), cardiomyocytes(2-4) and vascular smooth muscle cells(5), where they are involved in the regulation of heart rate(6), pulmonary artery tone(5,7), sleep/wake cycles(8) and responses to volatile anaesthetics(8-11). K-2P channels regulate the resting membrane potential, providing background K+ currents controlled by numerous physiological stimuli(12-15). Unlike other K-2P channels, TASK channels are able to bind inhibitors with high affinity, exceptional selectivity and very slow compound washout rates. As such, these channels are attractive drug targets, and TASK-1 inhibitors are currently in clinical trials for obstructive sleep apnoea and atrial fibrillation(16). In general, potassium channels have an intramembrane vestibule with a selectivity filter situated above and a gate with four parallel helices located below  however, the K-2P channels studied so far all lack a lower gate. Here we present the X-ray crystal structure of TASK-1, and show that it contains a lower gate-which we designate as an '  X-gate'  -created by interaction of the two crossed C-terminal M4 transmembrane helices at the vestibule entrance. This structure is formed by six residues ((VLRFMT248)-V-243) that are essential for responses to volatile anaesthetics(10), neurotransmitters(13) and G-protein-coupled receptors(13). Mutations within the X-gate and the surrounding regions markedly affect both the channel-open probability and the activation of the channel by anaesthetics. Structures of TASK-1 bound to two high-affinity inhibitors show that both compounds bind below the selectivity filter and are trapped in the vestibule by the X-gate, which explains their exceptionally low washout rates. The presence of the X-gate in TASK channels explains many aspects of their physiological and pharmacological behaviour, which will be beneficial for the future development and optimization of TASK modulators for the treatment of heart, lung and sleep disorders.


The X-ray crystal structure of the potassium channel TASK-1 reveals the presence of an X-gate, which traps small-molecule inhibitors in the intramembrane vestibule and explains their low washout rates from the channel.


  
The ABC exporter IrtAB imports and reduces mycobacterial siderophores 期刊论文
NATURE, 2020, 580 (7803) : 413-+
作者:  Fessler, Evelyn;  Eckl, Eva-Maria;  Schmitt, Sabine;  Mancilla, Igor Alves;  Meyer-Bender, Matthias F.;  Hanf, Monika;  Philippou-Massier, Julia;  Krebs, Stefan;  Zischka, Hans;  Jae, Lucas T.
收藏  |  浏览/下载:35/0  |  提交时间:2020/07/03

Intracellular replication of the deadly pathogen Mycobacterium tuberculosis relies on the production of small organic molecules called siderophores that scavenge iron from host proteins(1). M. tuberculosis produces two classes of siderophore, lipid-bound mycobactin and water-soluble carboxymycobactin(2,3). Functional studies have revealed that iron-loaded carboxymycobactin is imported into the cytoplasm by the ATP binding cassette (ABC) transporter IrtAB(4), which features an additional cytoplasmic siderophore interaction domain(5). However, the predicted ABC exporter fold of IrtAB is seemingly contradictory to its import function. Here we show that membrane-reconstituted IrtAB is sufficient to import mycobactins, which are then reduced by the siderophore interaction domain to facilitate iron release. Structure determination by X-ray crystallography and cryo-electron microscopy not only confirms that IrtAB has an ABC exporter fold, but also reveals structural peculiarities at the transmembrane region of IrtAB that result in a partially collapsed inward-facing substrate-binding cavity. The siderophore interaction domain is positioned in close proximity to the inner membrane leaflet, enabling the reduction of membrane-inserted mycobactin. Enzymatic ATPase activity and in vivo growth assays show that IrtAB has a preference for mycobactin over carboxymycobactin as its substrate. Our study provides insights into an unusual ABC exporter that evolved as highly specialized siderophore-import machinery in mycobacteria.


  
TLR9 and beclin 1 crosstalk regulates muscle AMPK activation in exercise 期刊论文
NATURE, 2020
作者:  Keener, Megan;  Hunt, Camden;  Carroll, Timothy G.;  Kampel, Vladimir;  Dobrovetsky, Roman;  Hayton, Trevor W.;  Menard, Gabriel
收藏  |  浏览/下载:33/0  |  提交时间:2020/07/03

In mice, the interaction of the innate immune sensor TLR9 with beclin 1 is shown to have a role in glucose metabolism and AMPK activation in skeletal muscle during exercise.


The activation of adenosine monophosphate-activated protein kinase (AMPK) in skeletal muscle coordinates systemic metabolic responses to exercise(1). Autophagy-a lysosomal degradation pathway that maintains cellular homeostasis(2)-is upregulated during exercise, and a core autophagy protein, beclin 1, is required for AMPK activation in skeletal muscle(3). Here we describe a role for the innate immune-sensing molecule Toll-like receptor 9 (TLR9)(4), and its interaction with beclin 1, in exercise-induced activation of AMPK in skeletal muscle. Mice that lack TLR9 are deficient in both exercise-induced activation of AMPK and plasma membrane localization of the GLUT4 glucose transporter in skeletal muscle, but are not deficient in autophagy. TLR9 binds beclin 1, and this interaction is increased by energy stress (glucose starvation and endurance exercise) and decreased by a BCL2 mutation(3,5) that blocks the disruption of BCL2-beclin 1 binding. TLR9 regulates the assembly of the endolysosomal phosphatidylinositol 3-kinase complex (PI3KC3-C2)-which contains beclin 1 and UVRAG-in skeletal muscle during exercise, and knockout of beclin 1 or UVRAG inhibits the cellular AMPK activation induced by glucose starvation. Moreover, TLR9 functions in a muscle-autonomous fashion in ex vivo contraction-induced AMPK activation, glucose uptake and beclin 1-UVRAG complex assembly. These findings reveal a heretofore undescribed role for a Toll-like receptor in skeletal-muscle AMPK activation and glucose metabolism during exercise, as well as unexpected crosstalk between this innate immune sensor and autophagy proteins.


  
Structure of the neurotensin receptor 1 in complex with beta-arrestin 1 期刊论文
NATURE, 2020, 579 (7798) : 303-+
作者:  Kollmorgen, Sepp;  Hahnloser, Richard H. R.;  Mante, Valerio
收藏  |  浏览/下载:34/0  |  提交时间:2020/07/03

Arrestin proteins bind to active, phosphorylated G-protein-coupled receptors (GPCRs), thereby preventing G-protein coupling, triggering receptor internalization and affecting various downstream signalling pathways(1,2). Although there is a wealth of structural information detailing the interactions between GPCRs and G proteins, less is known about how arrestins engage GPCRs. Here we report a cryo-electron microscopy structure of full-length human neurotensin receptor 1 (NTSR1) in complex with truncated human beta-arrestin 1 (beta arr1(Delta CT)). We find that phosphorylation of NTSR1 is critical for the formation of a stable complex with beta arr1(Delta CT), and identify phosphorylated sites in both the third intracellular loop and the C terminus that may promote this interaction. In addition, we observe a phosphatidylinositol-4,5-bisphosphate molecule forming a bridge between the membrane side of NTSR1 transmembrane segments 1 and 4 and the C-lobe of arrestin. Compared with a structure of a rhodopsin-arrestin-1 complex, in our structure arrestin is rotated by approximately 85 degrees relative to the receptor. These findings highlight both conserved aspects and plasticity among arrestin-receptor interactions.


  
Single-vesicle imaging reveals lipid-selective and stepwise membrane disruption by monomeric alpha-synuclein 期刊论文
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 2020, 117 (25) : 14178-14186
作者:  Hannestad, Jonas K.;  Rocha, Sandra;  Agnarsson, Bjorn;  Zhdanov, Vladimir P.;  Wittung-Stafshede, Pernilla;  Hook, Fredrik
收藏  |  浏览/下载:12/0  |  提交时间:2020/02/17
alpha-synuclein  single-vesicle scattering  lipid vesicle  membrane interaction