Editorials
ヒト組織を使った研究の規範を見直し、倫理問題に真剣に取り組み続けるべきだ。
A culture of consent p.407
More than 50 years after the WI-38 cell line was derived from a fetus, science and society has still to get to grips with the ethical issues of using human tissue in research.
doi: 10.1038/498407a
塩基配列解読技術が進み、研究者の家族のゲノムが、病気の新たな手がかりにつながる例が増えている。
Family first p.408
Better sequencing techniques are enabling some scientists to take personal genomics literally.
doi: 10.1038/498408a
現代社会の睡眠パターンは健康に悪影響を及ぼしており、健全な睡眠と休息について研究する必要がある。
How do you sleep? p.408
Modern sleep patterns cause ill health, so it is time to work out how much rest we really need.
doi: 10.1038/498408b
News
シェールガスの掘削が、地下水汚染の原因に。
Gas drilling taints groundwater p.415
Chemical analysis links methane in drinking wells to shale-gas extraction.
doi: 10.1038/498415a
新しい物質の利用で、リチウム–イオウ電池に再び脚光が。
Sulphur back in vogue for batteries p.416
Lithium–sulphur batteries benefit from new materials.
doi: 10.1038/498416a
HIVを除去して完治させる早期治療法が、小児を対象にした臨床試験へ。
Bid to cure HIV ramps up p.417
Clinical trial will aim to replicate virus-expunging therapy that worked in US infant.
doi: 10.1038/498417a
父である研究者の執念が実って、娘の遺伝的症候群の手がかりが明らかに。
Father’s genetic quest pays off p.418
Mutation provides clue to daughter’s undefined syndrome.
doi: 10.1038/498418a
理論的研究によって、量子論の不確定性原理が、より確実に。
Proof mooted for quantum uncertainty p.419
Study confirms principle’s limits on measurement accuracy.
doi: 10.1038/498419a
巧みな観測装置を使って、海洋酸性化が生態系に与える影響の調査が。
Floating tubes test sea-life sensitivity p.420
Ocean labs probe effects of ocean acidification on ecosystems.
doi: 10.1038/498420a
News Features
医学研究：細胞分裂
Medical research: Cell division p.422
1962年に作られたWI-38細胞は、ワクチン生産や老化研究に重要な役割を果たしてきたが、中絶胎児の細胞由来という点で倫理的議論の種にもなっている。
doi: 10.1038/498422a
News & Views
量子物理学：微かな動きが集合する
Quantum physics: Spooky action gets collective p.438
気体中の非常に多数の原子が、単一のリュードベリ励起状態を共有することがある。このような励起状態と単一光子の間で起こる量子もつれが今回、決定論的に実証された。
doi: 10.1038/nature12259
再生生物学：心臓が壊れた胚を癒す
Regenerative biology: Heartbroken embryos heal p.439
ゼブラフィッシュ胚では、心臓の一部が損傷を受けると、隣接領域から供給される細胞を使って修復が行われる。再生に関わるこのような細胞は中間前駆細胞集団に起源を持つらしい。
doi: 10.1038/nature12262
応用物理学：熱を覆い隠す
Applied physics: Cloaking of heat p.440
はるか昔から、衣類は保温・断熱のために使われてきた。熱の流れは維持しながら熱を遮蔽する、つまり熱センサーから対象を隠せる遮蔽装置が、今回実証された。
doi: 10.1038/498440a
神経科学：時差が異なる幹細胞
Neuroscience: Stem cells in multiple time zones p.441
ショウジョウバエの幼虫では、神経幹細胞が異なる時点で異なる細胞種を作り出している。このような時間的進行は遺伝子転写因子が作る複数のカスケードによって制御されていることが明らかになった。
doi: 10.1038/nature12261
エレクトロニクス：カーボンナノチューブトランジスターへの道
Electronics: The road to carbon nanotube transistors p.443
カーボンナノチューブを精製し、配置することは、こうしたナノ材料を使った電子デバイスを作る際の難問である。こうした分野での最近の進歩によって、トランジスター技術につながる面白い道が切り開かれそうな勢いが見えてきた。
doi: 10.1038/498443a
細胞間シグナル伝達：がんは栄養の有無を感知できない
Cell signalling: Nutrient sensing lost in cancer p.444
細胞は、栄養の入手可能性の変動を感知し、それに応答することができる。このような栄養情報を細胞増殖装置に伝える経路を破壊する変異は、がん細胞の制御を受けない増殖の一因となっているらしい。
doi: 10.1038/498444a
動物行動：脳の食物
Animal behaviour: Brain food p.446
単独性の動物では、学習と記憶は大きなエネルギー消費を伴うので、エネルギー源が不足するとこのような認知機能が損なわれることがある。ミツバチでの研究から、このような影響は集団を作って生活している動物でも起こることがわかった。
doi: 10.1038/498446a
疫学：マラリアの薬剤耐性をマッピング
Epidemiology: Resistance mapping in malaria p.446
ヒトに寄生するマラリア原虫の全ゲノム塩基配列解読から、アルテミシニンを使った薬剤に対する耐性に関連するゲノム領域が明らかになった。この知見は、アルテミシニン耐性というこの憂慮すべき傾向の起源と広がりを説明するのに役立ちそうだ。
doi: 10.1038/498446b
フォトニクス：とびきり小型のシリコンレーザー
Photonics: An ultra-small silicon laser p.447
電子産業で最も広く見られる材料であるシリコンを使って、マイクロメートルサイズのレーザーが作られた。このデバイスは、数マイクロワット程度の電力で作動し、コンパクトな光集積回路への道を開く可能性がある。
doi: 10.1038/498447a
Articles
発生：前駆細胞の組み合わせ的な時間的パターン化が神経系の多様性を拡大する
Combinatorial temporal patterning in progenitors expands neural diversity p.449
Drosophila neural stem cells and their proliferative progeny are both shown to change over time, thus increasing the diversity of their neuronal and glial progeny; such temporal patterning may also contribute to neuronal complexity in the human neocortex.
doi: 10.1038/nature12266
発生：ショウジョウバエのメダラ神経芽細胞の時間的パターン化が神経運命を制御する
Temporal patterning of Drosophila medulla neuroblasts controls neural fates p.456
Five transcription factors are sequentially expressed in a temporal cascade in Drosophila medulla neuroblasts of the visual system; cross-regulations between these transcription factors control the temporal transitions, and temporal switching of neural progenitors may be a common theme in neuronal specification, with different sequences of transcription factors being used in different contexts.
doi: 10.1038/nature12319
Letters
宇宙：食連星系における外層を剥ぎ取られた赤色巨星の多重周期の脈動
Multi-periodic pulsations of a stripped red-giant star in an eclipsing binary system p.463
Low-mass white-dwarf stars are the remnants of disrupted red-giant stars in binary millisecond pulsars and other exotic binary star systems. Some low-mass white dwarfs cool rapidly, whereas others stay bright for millions of years because of stable fusion in thick surface hydrogen layers. This dichotomy is not well understood, so the potential use of low-mass white dwarfs as independent clocks with which to test the spin-down ages of pulsars or as probes of the extreme environments in which low-mass white dwarfs form cannot fully be exploited. Here we report precise mass and radius measurements for the precursor to a low-mass white dwarf. We find that only models in which this disrupted red-giant star has a thick hydrogen envelope can match the strong constraints provided by our data. Very cool low-mass white dwarfs must therefore have lost their thick hydrogen envelopes by irradiation from pulsar companions or by episodes of unstable hydrogen fusion (shell flashes). We also find that this low-mass white-dwarf precursor is a type of pulsating star not hitherto seen. The observed pulsation frequencies are sensitive to internal processes that determine whether this star will undergo shell flashes.
doi: 10.1038/nature12192
量子物理学：光と光学的原子励起の量子もつれ
Entanglement between light and an optical atomic excitation p.466
The generation, distribution and control of entanglement across quantum networks is one of the main goals of quantum information science. In previous studies, hyperfine ground states of single atoms or atomic ensembles have been entangled with spontaneously emitted light. The probabilistic character of the spontaneous emission process leads to long entanglement generation times, limiting realized network implementations to just two nodes. The success probability for atom–photon entanglement protocols can be increased by confining a single atom in a high-finesse optical cavity. Alternatively, quantum networks with superior scaling properties could be achieved using entanglement between light fields and atoms in quantum superpositions of the ground and highly excited (Rydberg) electronic states. Here we report the generation of such entanglement. The dephasing of the optical atomic coherence is inhibited by state-insensitive confinement of both the ground and Rydberg states of an ultracold atomic gas in an optical lattice. Our results pave the way for functional, many-node quantum networks capable of deterministic quantum logic operations between long-lived atomic memories.
doi: 10.1038/nature12227
フォトニクス：マイクロワットしきい値のマイクロメートルスケール・シリコンラマンレーザー
A micrometre-scale Raman silicon laser with a microwatt threshold p.470
The application of novel technologies to silicon electronics has been intensively studied with a view to overcoming the physical limitations of Moore’s law, that is, the observation that the number of components on integrated chips tends to double every two years. For example, silicon devices have enormous potential for photonic integrated circuits on chips compatible with complementary metal–oxide–semiconductor devices, with various key elements having been demonstrated in the past decade. In particular, a focus on the exploitation of the Raman effect has added active optical functionality to pure silicon, culminating in the realization of a continuous-wave all-silicon laser. This achievement is an important step towards silicon photonics, but the desired miniaturization to micrometre dimensions and the reduction of the threshold for laser action to microwatt powers have yet to be achieved: such lasers remain limited to centimetre-sized cavities with thresholds higher than 20 milliwatts, even with the assistance of reverse-biased p–i–n diodes. Here we demonstrate a continuous-wave Raman silicon laser using a photonic-crystal, high-quality-factor nanocavity without any p–i–n diodes, yielding a device with a cavity size of less than 10 micrometres and an unprecedentedly low lasing threshold of 1 microwatt. Our nanocavity design exploits the principle that the strength of light–matter interactions is proportional to the ratio of quality factor to the cavity volume and allows drastic enhancement of the Raman gain beyond that predicted theoretically. Such a device may make it possible to construct practical silicon lasers and amplifiers for large-scale integration in photonic circuits.
doi: 10.1038/nature12237
地球：河川浸食と地すべりとの間のフィードバックによって決まる山脈の寿命
Lifespan of mountain ranges scaled by feedbacks between landsliding and erosion by rivers p.475
An important challenge in geomorphology is the reconciliation of the high fluvial incision rates observed in tectonically active mountain ranges with the long-term preservation of significant mountain-range relief in ancient, tectonically inactive orogenic belts. River bedrock erosion and sediment transport are widely recognized to be the principal controls on the lifespan of mountain ranges. But the factors controlling the rate of erosion and the reasons why they seem to vary significantly as a function of tectonic activity remain controversial. Here we use computational simulations to show that the key to understanding variations in the rate of erosion between tectonically active and inactive mountain ranges may relate to a bidirectional coupling between bedrock river incision and landslides. Whereas fluvial incision steepens surrounding hillslopes and increases landslide frequency, landsliding affects fluvial erosion rates in two fundamentally distinct ways. On the one hand, large landslides overwhelm the river transport capacity and cause upstream build up of sediment that protects the river bed from further erosion. On the other hand, in delivering abrasive agents to the streams, landslides help accelerate fluvial erosion. Our models illustrate how this coupling has fundamentally different implications for rates of fluvial incision in active and inactive mountain ranges. The coupling therefore provides a plausible physical explanation for the preservation of significant mountain-range relief in old orogenic belts, up to several hundred million years after tectonic activity has effectively ceased.
doi: 10.1038/nature12218
地球：プレート運動の正味の特性により明らかになった活動的なマントル上昇流の安定性
Stability of active mantle upwelling revealed by net characteristics of plate tectonics p.479
Viscous convection within the mantle is linked to tectonic plate motions and deforms Earth’s surface across wide areas. Such close links between surface geology and deep mantle dynamics presumably operated throughout Earth’s history, but are difficult to investigate for past times because the history of mantle flow is poorly known. Here we show that the time dependence of global-scale mantle flow can be deduced from the net behaviour of surface plate motions. In particular, we tracked the geographic locations of net convergence and divergence for harmonic degrees 1 and 2 by computing the dipole and quadrupole moments of plate motions from tectonic reconstructions extended back to the early Mesozoic era. For present-day plate motions, we find dipole convergence in eastern Asia and quadrupole divergence in both central Africa and the central Pacific. These orientations are nearly identical to the dipole and quadrupole orientations of underlying mantle flow, which indicates that these ‘net characteristics’ of plate motions reveal deeper flow patterns. The positions of quadrupole divergence have not moved significantly during the past 250 million years, which suggests long-term stability of mantle upwelling beneath Africa and the Pacific Ocean. These upwelling locations are positioned above two compositionally and seismologically distinct regions of the lowermost mantle, which may organize global mantle flow as they remain stationary over geologic time.
doi: 10.1038/nature12203
進化：ヒト属の肩の弾性エネルギー保存と高速投てきの進化
Elastic energy storage in the shoulder and the evolution of high-speed throwing in Homo p.483
Some primates, including chimpanzees, throw objects occasionally, but only humans regularly throw projectiles with high speed and accuracy. Darwin noted that the unique throwing abilities of humans, which were made possible when bipedalism emancipated the arms, enabled foragers to hunt effectively using projectiles. However, there has been little consideration of the evolution of throwing in the years since Darwin made his observations, in part because of a lack of evidence of when, how and why hominins evolved the ability to generate high-speed throws. Here we use experimental studies of humans throwing projectiles to show that our throwing capabilities largely result from several derived anatomical features that enable elastic energy storage and release at the shoulder. These features first appear together approximately 2 million years ago in the species Homo erectus. Taking into consideration archaeological evidence suggesting that hunting activity intensified around this time, we conclude that selection for throwing as a means to hunt probably had an important role in the evolution of the genus Homo.
doi: 10.1038/nature12267
神経生物学：orcoが変異した蚊は、ヒトに対する強い宿主選択性を失い、揮発性の昆虫忌避剤DEETの忌避効果を受けなくなる
orco mutant mosquitoes lose strong preference for humans and are not repelled by volatile DEET p.487
Female mosquitoes of some species are generalists and will blood-feed on a variety of vertebrate hosts, whereas others display marked host preference. Anopheles gambiae and Aedes aegypti have evolved a strong preference for humans, making them dangerously efficient vectors of malaria and Dengue haemorrhagic fever. Specific host odours probably drive this strong preference because other attractive cues, including body heat and exhaled carbon dioxide (CO2), are common to all warm-blooded hosts. Insects sense odours via several chemosensory receptor families, including the odorant receptors (ORs), membrane proteins that form heteromeric odour-gated ion channels comprising a variable ligand-selective subunit and an obligate co-receptor called Orco (ref. 6). Here we use zinc-finger nucleases to generate targeted mutations in the orco gene of A. aegypti to examine the contribution of Orco and the odorant receptor pathway to mosquito host selection and sensitivity to the insect repellent DEET (N,N-diethyl-meta-toluamide). orco mutant olfactory sensory neurons have greatly reduced spontaneous activity and lack odour-evoked responses. Behaviourally, orco mutant mosquitoes have severely reduced attraction to honey, an odour cue related to floral nectar, and do not respond to human scent in the absence of CO2. However, in the presence of CO2, female orco mutant mosquitoes retain strong attraction to both human and animal hosts, but no longer strongly prefer humans. orco mutant females are attracted to human hosts even in the presence of DEET, but are repelled upon contact, indicating that olfactory- and contact-mediated effects of DEET are mechanistically distinct. We conclude that the odorant receptor pathway is crucial for an anthropophilic vector mosquito to discriminate human from non-human hosts and to be effectively repelled by volatile DEET.
doi: 10.1038/nature12206
医学：EndMTは脳海綿状血管腫の開始と進行に関与する
EndMT contributes to the onset and progression of cerebral cavernous malformations p.492
Cerebral cavernous malformation (CCM) is a vascular dysplasia, mainly localized within the brain and affecting up to 0.5% of the human population. CCM lesions are formed by enlarged and irregular blood vessels that often result in cerebral haemorrhages. CCM is caused by loss-of-function mutations in one of three genes, namely CCM1 (also known as KRIT1), CCM2 (OSM) and CCM3 (PDCD10), and occurs in both sporadic and familial forms. Recent studies have investigated the cause of vascular dysplasia and fragility in CCM, but the in vivo functions of this ternary complex remain unclear. Postnatal deletion of any of the three Ccm genes in mouse endothelium results in a severe phenotype, characterized by multiple brain vascular malformations that are markedly similar to human CCM lesions. Endothelial-to-mesenchymal transition (EndMT) has been described in different pathologies, and it is defined as the acquisition of mesenchymal- and stem-cell-like characteristics by the endothelium. Here we show that endothelial-specific disruption of the Ccm1 gene in mice induces EndMT, which contributes to the development of vascular malformations. EndMT in CCM1-ablated endothelial cells is mediated by the upregulation of endogenous BMP6 that, in turn, activates the transforming growth factor-β (TGF-β) and bone morphogenetic protein (BMP) signalling pathway. Inhibitors of the TGF-β and BMP pathway prevent EndMT both in vitro and in vivo and reduce the number and size of vascular lesions in CCM1-deficient mice. Thus, increased TGF-β and BMP signalling, and the consequent EndMT of CCM1-null endothelial cells, are crucial events in the onset and progression of CCM disease. These studies offer novel therapeutic opportunities for this severe, and so far incurable, pathology.
doi: 10.1038/nature12207
発生：in vivoでの心臓の再プログラム化がゼブラフィッシュの心臓再生に寄与する
In vivo cardiac reprogramming contributes to zebrafish heart regeneration p.497
Despite current treatment regimens, heart failure remains the leading cause of morbidity and mortality in the developed world due to the limited capacity of adult mammalian ventricular cardiomyocytes to divide and replace ventricular myocardium lost from ischaemia-induced infarct. Hence there is great interest to identify potential cellular sources and strategies to generate new ventricular myocardium. Past studies have shown that fish and amphibians and early postnatal mammalian ventricular cardiomyocytes can proliferate to help regenerate injured ventricles; however, recent studies have suggested that additional endogenous cellular sources may contribute to this overall ventricular regeneration. Here we have developed, in the zebrafish (Danio rerio), a combination of fluorescent reporter transgenes, genetic fate-mapping strategies and a ventricle-specific genetic ablation system to discover that differentiated atrial cardiomyocytes can transdifferentiate into ventricular cardiomyocytes to contribute to zebrafish cardiac ventricular regeneration. Using in vivo time-lapse and confocal imaging, we monitored the dynamic cellular events during atrial-to-ventricular cardiomyocyte transdifferentiation to define intermediate cardiac reprogramming stages. We observed that Notch signalling becomes activated in the atrial endocardium following ventricular ablation, and discovered that inhibiting Notch signalling blocked the atrial-to-ventricular transdifferentiation and cardiac regeneration. Overall, these studies not only provide evidence for the plasticity of cardiac lineages during myocardial injury, but more importantly reveal an abundant new potential cardiac resident cellular source for cardiac ventricular regeneration.
doi: 10.1038/nature12322
医学：重症マラリアには内皮プロテインC受容体への原虫の結合が関係している
Severe malaria is associated with parasite binding to endothelial protein C receptor p.502
Sequestration of Plasmodium falciparum-infected erythrocytes in host blood vessels is a key triggering event in the pathogenesis of severe childhood malaria, which is responsible for about one million deaths every year. Sequestration is mediated by specific interactions between members of the P. falciparum erythrocyte membrane protein 1 (PfEMP1) family and receptors on the endothelial lining. Severe childhood malaria is associated with expression of specific PfEMP1 subtypes containing domain cassettes (DCs) 8 and 13 (ref. 3), but the endothelial receptor for parasites expressing these proteins was unknown. Here we identify endothelial protein C receptor (EPCR), which mediates the cytoprotective effects of activated protein C, as the endothelial receptor for DC8 and DC13 PfEMP1. We show that EPCR binding is mediated through the amino-terminal cysteine-rich interdomain region (CIDRα1) of DC8 and group A PfEMP1 subfamilies, and that CIDRα1 interferes with protein C binding to EPCR. This PfEMP1 adhesive property links P. falciparum cytoadhesion to a host receptor involved in anticoagulation and endothelial cytoprotective pathways, and has implications for understanding malaria pathology and the development of new malaria interventions.
doi: 10.1038/nature12216
免疫：BACH2はエフェクタープログラムを抑制してTregを介した免疫恒常性を安定化する
BACH2 represses effector programs to stabilize Treg-mediated immune homeostasis p.506
Through their functional diversification, distinct lineages of CD4+ T cells can act to either drive or constrain immune-mediated pathology. Transcription factors are critical in the generation of cellular diversity, and negative regulators antagonistic to alternate fates often act in conjunction with positive regulators to stabilize lineage commitment. Genetic polymorphisms within a single locus encoding the transcription factor BACH2 are associated with numerous autoimmune and allergic diseases including asthma, Crohn’s disease, coeliac disease, vitiligo, multiple sclerosis and type 1 diabetes. Although these associations point to a shared mechanism underlying susceptibility to diverse immune-mediated diseases, a function for BACH2 in the maintenance of immune homeostasis has not been established. Here, by studying mice in which the Bach2 gene is disrupted, we define BACH2 as a broad regulator of immune activation that stabilizes immunoregulatory capacity while repressing the differentiation programs of multiple effector lineages in CD4+ T cells. BACH2 was required for efficient formation of regulatory (Treg) cells and consequently for suppression of lethal inflammation in a manner that was Treg-cell-dependent. Assessment of the genome-wide function of BACH2, however, revealed that it represses genes associated with effector cell differentiation. Consequently, its absence during Treg polarization resulted in inappropriate diversion to effector lineages. In addition, BACH2 constrained full effector differentiation within TH1, TH2 and TH17 cell lineages. These findings identify BACH2 as a key regulator of CD4+ T-cell differentiation that prevents inflammatory disease by controlling the balance between tolerance and immunity.
doi: 10.1038/nature12199
分子生物学：Rev-Erbは、エンハンサーに由来する転写の阻害により、マクロファージの遺伝子発現を抑制する
Rev-Erbs repress macrophage gene expression by inhibiting enhancer-directed transcription p.511
Rev-Erb-α and Rev-Erb-β are nuclear receptors that regulate the expression of genes involved in the control of circadian rhythm, metabolism and inflammatory responses. Rev-Erbs function as transcriptional repressors by recruiting nuclear receptor co-repressor (NCoR)–HDAC3 complexes to Rev-Erb response elements in enhancers and promoters of target genes, but the molecular basis for cell-specific programs of repression is not known. Here we present evidence that in mouse macrophages Rev-Erbs regulate target gene expression by inhibiting the functions of distal enhancers that are selected by macrophage-lineage-determining factors, thereby establishing a macrophage-specific program of repression. Remarkably, the repressive functions of Rev-Erbs are associated with their ability to inhibit the transcription of enhancer-derived RNAs (eRNAs). Furthermore, targeted degradation of eRNAs at two enhancers subject to negative regulation by Rev-Erbs resulted in reduced expression of nearby messenger RNAs, suggesting a direct role of these eRNAs in enhancer function. By precisely defining eRNA start sites using a modified form of global run-on sequencing that quantifies nascent 5′ ends, we show that transfer of full enhancer activity to a target promoter requires both the sequences mediating transcription-factor binding and the specific sequences encoding the eRNA transcript. These studies provide evidence for a direct role of eRNAs in contributing to enhancer functions and suggest that Rev-Erbs act to suppress gene expression at a distance by repressing eRNA transcription.
doi: 10.1038/nature12209
分子生物学：エンハンサーRNAがエストロゲン依存的転写活性化に果たす機能的役割
Functional roles of enhancer RNAs for oestrogen-dependent transcriptional activation p.516
The functional importance of gene enhancers in regulated gene expression is well established. In addition to widespread transcription of long non-coding RNAs (lncRNAs) in mammalian cells, bidirectional ncRNAs are transcribed on enhancers, and are thus referred to as enhancer RNAs (eRNAs). However, it has remained unclear whether these eRNAs are functional or merely a reflection of enhancer activation. Here we report that in human breast cancer cells 17β-oestradiol (E2)-bound oestrogen receptor α (ER-α) causes a global increase in eRNA transcription on enhancers adjacent to E2-upregulated coding genes. These induced eRNAs, as functional transcripts, seem to exert important roles for the observed ligand-dependent induction of target coding genes, increasing the strength of specific enhancer–promoter looping initiated by ER-α binding. Cohesin, present on many ER-α-regulated enhancers even before ligand treatment, apparently contributes to E2-dependent gene activation, at least in part by stabilizing E2/ER-α/eRNA-induced enhancer–promoter looping. Our data indicate that eRNAs are likely to have important functions in many regulated programs of gene transcription.
doi: 10.1038/nature12210
構造生物学：C型肝炎ウイルス由来p7チャネルの珍しい構造
Unusual architecture of the p7 channel from hepatitis C virus p.521
The hepatitis C virus (HCV) has developed a small membrane protein, p7, which remarkably can self-assemble into a large channel complex that selectively conducts cations. We wanted to examine the structural solution that the viroporin adopts in order to achieve selective cation conduction, because p7 has no homology with any of the known prokaryotic or eukaryotic channel proteins. The activity of p7 can be inhibited by amantadine and rimantadine, which are potent blockers of the influenza M2 channel and licensed drugs against influenza infections. The adamantane derivatives have been used in HCV clinical trials, but large variation in drug efficacy among the various HCV genotypes has been difficult to explain without detailed molecular structures. Here we determine the structures of this HCV viroporin as well as its drug-binding site using the latest nuclear magnetic resonance (NMR) technologies. The structure exhibits an unusual mode of hexameric assembly, where the individual p7 monomers, i, not only interact with their immediate neighbours, but also reach farther to associate with the i+2 and i+3 monomers, forming a sophisticated, funnel-like architecture. The structure also points to a mechanism of cation selection: an asparagine/histidine ring that constricts the narrow end of the funnel serves as a broad cation selectivity filter, whereas an arginine/lysine ring that defines the wide end of the funnel may selectively allow cation diffusion into the channel. Our functional investigation using whole-cell channel recording shows that these residues are critical for channel activity. NMR measurements of the channel–drug complex revealed six equivalent hydrophobic pockets between the peripheral and pore-forming helices to which amantadine or rimantadine binds, and compound binding specifically to this position may allosterically inhibit cation conduction by preventing the channel from opening. Our data provide a molecular explanation for p7-mediated cation conductance and its inhibition by adamantane derivatives.
doi: 10.1038/nature12283
