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Cryo-EM structure of the mature dengue virus at 3.5- resolution
Xiaokang Zhang15,9, Peng Ge13,9, Xuekui Yu13, Jennifer M Brannan3,8, Guoqiang Bi4,5, Qinfen Zhang6, Stan Schein2,7 & Z Hong Zhou15
RegulatedbypH,membrane-anchoredproteinsEandMfunctionduringdenguevirusmaturationandmembranefusion. Ouratomicmodelofthewholevirionfromcryoelectronmicroscopyat3.5-resolutionrevealsthatinthematurevirusat neutralextracellularpH,theN-terminal20-amino-acidsegmentofM(involvingthreepH-sensinghistidines)latchesandthereby preventsspring-loadedEfusionproteinfromprematurelyexposingitsfusionpeptide.ThisMlatchisfastenedatanearlierstage, duringmaturationatacidicpHinthetrans-Golginetwork.Atalaterstage,toinitiateinfectioninresponsetoacidicpHinthe lateendosome,Mreleasesthelatchandexposesthefusionpeptide.Thus,MservesasamultistepchaperoneofEtocontrolthe conformationalchangesaccompanyingmaturationandinfection.ThesepH-sensitiveinteractionscouldserveastargetsfor drugdiscovery.
npg 2013 Nature America, Inc. All rights reserved.
Dengue virus is a prevalent mosquito-borne flavivirus that is endemic across tropical and subtropical regions, causing diseases ranging from self-limiting fever to lethal hemorrhagic fever and shock. Each year, more than 50 million people are infected1. Dengue virus is also a potential biothreat agent2. Currently, there are neither licensed vaccines nor specific antiviral therapies against dengue infection. Indeed, the spread of dengue virus is recognized as a major urban public health concern by the World Health Organization1.
Viral membrane proteins have critical roles during the life cycle of enveloped viruses such as the dengue virus, particularly during entry into a host cell. The two dengue virus membrane proteins, E and M, undergo dramatic structural changes from the immature to the mature, fusogenic form of the virion3 and then again at the time of infection. These two proteins are expressed in a polyprotein that is cleaved to yield the precursor of M (prM, consisting of M and a leading segment, pr) and E4. Then, upon exposure to the neutral pH of the endoplasmic reticulum, prM binds to E to form the spiky immature form of the virus3, the spikes consisting of trimers of the outward pointing domain II of E. E and prM then undergo further maturation that includes three steps: (i) triggered by low pH in the trans-Golgi network (TGN), formation of pr-stabilized dimers of E lying on the surface, producing the smooth immature virus3; (ii) cleavage of prM by the furin protease in the TGN into the pr and M portions4; and (iii) triggered by neutral pH in the extracellular space, shedding of pr upon release from the cell to yield the fusion-competent, smooth mature virion3. Later, during infection, dengue virus enters the cell
through receptor-mediated endocytosis, and fusion of virus membrane with endosomal membrane is triggered by low pH in the late endosome5,6. Although cryo-EM has provided low-resolution in situ structures of immature viruses and of mature virions7,8, and X-ray...