综述与专论：ESCRT复合体在细胞质膜损伤修复中的功能

细胞膜损伤在骨骼肌、血管内皮及胃肠道上皮等组织较为常见，及时有效的细胞膜修复（plasma membrane repair,PMR）能够保证细胞存活，反之，细胞则可能“死亡”。PMR由许多“修补匠”协同完成，它们分工明确且呈现出一定的时序特点。转运必需内体分选复合体（endosomal sorting complex required for transport,ESCRT）是近年来研究发现的在细胞膜损伤修复中发挥关键作用的“修补匠”，其由ESCRT-0、ESCRT-Ⅰ、ESCRT-Ⅱ、ESCRT-Ⅲ、Vps4-Vta1及ALIX组成，主要参与胞外出芽（budding）和多囊泡体（multivesicular body,MVB）形成两种修复途径。本文详细综述了ESCRT系统介导细胞膜损伤修复的可能机制，以期为细胞膜损伤的治疗靶点筛选及促恢复手段创新提供理论依据。     

TSG101在病毒出芽过程中的作用及其机制

TSG101基因是新发现的抑癌基因候选者,定位于人类 11号染色体 p1511-p1512,其编码产物TSG101蛋白N端区域与泛素结合酶(UBC)同源。近年来研究发现,TSG101基因具有多种重要的功能,与多种病毒出芽密切相关,所以TSG101可作为一个新的抗病毒靶点。本文主要从TSG101在多种病毒（HIV、IAV、MARV、ASV等）出芽过程中扮演的角色,TSG101与多种蛋白(泛素、Nedd4、ARMMs、Tom1、Gag、VP40、NP等)的相互作用进而辅助病毒出芽的机制,以及TSG101抑制剂的研究等方面进行阐述。     

多囊体生物发生和蛋白质分拣——ESCRT、Vps4、Ubiquitination一个都不能少

多囊体(multivesicular body,MVB)是由晚期内吞体的限制膜内陷出芽而形成的动态的亚细胞结构,是真核细胞重要的膜和蛋白质运输与分拣中心,并与信号转导、胞质分裂、基因沉默、自噬、蛋白质的质量控制、病毒出芽等密切相关.多囊体生物发生涉及20多种囊泡分拣蛋白(Vps),最重要的是在内吞体膜上形成的4种内吞体运输分拣复合物(ESCRT 0、Ⅰ、Ⅱ、Ⅲ)和Vps4.ESCRT 0与包涵素在内吞体膜上形成微域并富集泛素化的货物蛋白.ESCRTⅠ和Ⅱ诱导MVB囊泡出芽、促进囊泡形成并分拣货物蛋白到囊泡中.ESCRTⅢ收缩及剪切芽颈,完成最后的膜脱落过程.Vps4解离ESCRT以循环利用.泛素化及泛素化蛋白也能修饰或调控ESCRT的定位及功能.这些研究表明,泛素化蛋白、ESCRT和Vps4在内吞体膜上的相继协同作用是驱动紧密偶联的多囊体生物发生及蛋白质分拣的主要力量.本文以蛋白质-蛋白质相互作用为主,综述了ESCRT复合物及Vps4多聚体的组装机制、相互作用、生理功能以及泛素化蛋白和泛素化对ESCRT的调控,并对下一步研究进行了展望.     

病毒包涵体在病毒感染细胞中的作用

病毒包涵体(viral inclusion bodies,IBs)是病毒蛋白在胞质或核内的聚集体,许多病毒能够形成病毒包涵体。早期研究认为,病毒包涵体只是病毒复制及组装的重要起始位点,然而最近研究发现,一些病毒形成的病毒包涵体在宿主细胞抗病毒免疫反应中具有一定作用。本文主要就病毒包涵体在病毒感染细胞中的作用进行综述。     

逆转运复合体在病毒生命周期中的作用

逆转运复合体(retromer)作为一种蛋白复合物,参与蛋白质从内体到反面高尔基体的逆向运输或从内体到质膜的回收过程,调节了细胞内货物的丰度及亚细胞分布.近期研究发现,retromer可与一些病毒蛋白相互作用从而影响病毒的生命周期.本文通过总结retromer与丙肝病毒、人类免疫缺陷病毒、人乳头瘤病毒、痘苗病毒以及松鼠猴疱疹病毒的相互作用,探讨retromer在病毒侵染中的作用.     

棉铃虫核型多角体病毒在生态环境中的滞留及作用

棉铃虫核型多角体病毒杀虫剂可湿性粉剂防治第三代棉铃虫,防治效果为８６．２％。使用酶联免疫法（ＥＬＩＳＡ）检测棉铃虫核型多角体病毒在土壤中的滞留,结果表明：施用病毒杀虫剂１、３、５、７天和两个月后都可检测到该病毒的存在。１９９３年９月上旬从河南封丘棉田采集的露水,ＰＨ为７．９８,病毒多角体在露水中保存３天,其生物活性无明显下降。     

中国棉铃虫核型多角体病毒VHA_(273)原毒株及其克隆株的比较研究

本文从形态结构、生物活性、核酸限制性内切酶图谱、结构多肽等方面对中国棉铃虫核型多角体病毒(HaNPV)VHA273多粒包埋型原毒株及其单粒包埋型克隆株H9进行了比较研究.它们对中国棉铃虫三龄初幼虫的LC5o值分别为2.987×104PIBs/mL和1.647×104PIBs/mL当感染剂量为2×107PIBs/mL时,其LT5o值分别是4.866d和4.797d.两个毒株的生物活性差别不大.经SDS-PAGE分析,两毒株结构多肽图谱带型相差较大.两毒株基因组经EcoR Ⅰ,BamH Ⅰ,Hind Ⅲ和Xba Ⅰ消化后,得到的内切酶图谱表现为两毒株间有差别.这些差异的发现将有助于从分子水平揭示多粒包埋病毒和单粒包埋病毒形成原因.     

蓝藻病毒(噬藻体)的研究进展

蓝藻(Bule-green algae)是一类原核生物,具有细菌的一些特征,因此又常称为蓝细菌(Cyanobacterium),相应地,把感染蓝细菌的病毒称为噬藻体(Cyanophage)[1～2],这是由于噬藻体与噬菌体非常相似的缘故.除蓝藻外,所有其它的藻类均是真核生物,通常将感染真核藻类的病毒称作"藻病毒"(Phycovirus)[3],它们的绝大多数是多角体的粒子(Polyhedral particles),只有个别如珊瑚轮藻(Chara corallina)病毒是杆状的[4].真核藻类病毒和病毒类粒子(VLPs)前文有过综述[4],蓝藻病毒或噬藻体则完全不同于真核藻类的病毒,二者是藻类病毒的重要组成部分,蓝藻病毒的研究情况有必要专门介绍.     

内质网和细胞骨架在植物病毒细胞内转运中的作用

植物病毒的侵染循环是一个病毒.寄主互作过程.内质网和细胞骨架在病毒细胞内转运中起着重要调节作用,不仅协助病毒从复制位点转运到细胞边缘胞间连丝处,还可能介导多余病毒因子的降解.针对植物细胞内质网和细胞骨架在烟草花叶病毒等植物病毒细胞内转运过程中所起的作用进行了综述.     

RetroCHMP3 blocks budding of enveloped viruses without blocking cytokinesis

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Mechanisms of enveloped RNA virus budding

To spread infection, enveloped viruses must bud from infected host cells. Recent research indicates that HIV and other enveloped RNA viruses bud by appropriating the cellular machinery that is normally used to create vesicles that bud into late endosomal compartments called multivesicular bodies. This new model of virus budding has many potential implications for cell biology and viral pathogenesis.     

A protein's final ESCRT

In eukaryotic cells, delivery of transmembrane proteins into the lumen of the lysosome for degradation is mediated by the multivesicular body pathway. The function of the ESCRT protein complexes is required for both the formation of multivesicular body lumenal vesicles and the sorting of endosomal cargo proteins into these vesicles. Recent studies have identified additional factors that seem to function as an upstream cargo retention system feeding into the ESCRT machinery, given new insights into the dynamic structure of multivesicular bodies, and identified a potential mechanism for multivesicular body vesicle formation.     

The ESCRT machinery: From the plasma membrane to endosomes and back again

Abstract

The manipulation and reorganization of lipid bilayers are required for diverse cellular processes, ranging from organelle biogenesis to cytokinetic abscission, and often involves transient membrane disruption. A set of membrane-associated proteins collectively known as the endosomal sorting complex required for transport (ESCRT) machinery has been implicated in membrane scission steps, which transform a single, continuous bilayer into two distinct bilayers, while simultaneously segregating cargo throughout the process. Components of the ESCRT pathway, which include 5 distinct protein complexes and an array of accessory factors, each serve discrete functions. This review focuses on the molecular mechanisms by which the ESCRT proteins facilitate cargo sequestration and membrane remodeling and highlights their unique roles in cellular homeostasis.     

ESCRT & Co

Components of the ESCRT (endosomal sorting complex required for transport) machinery mediate endosomal sorting of ubiquitinated membrane proteins. They are key regulators of biological processes important for cell growth and survival, such as growth‐factor‐mediated signalling and cytokinesis. In addition, enveloped viruses, such as HIV‐1, hijack and utilize the ESCRTs for budding during virus release and infection. Obviously, the ESCRT‐facilitated pathways require tight regulation, which is partly mediated by a group of interacting proteins, for which our knowledge is growing. In this review we discuss the different ESCRT‐modulating proteins and how they influence ESCRT‐dependent processes, for example, by acting as positive or negative regulators or by providing temporal and spatial control. A number of the interactors influence the classical ESCRT‐mediated process of endosomal cargo sorting, for example, by modulating the interaction between ubiquitinated cargo and the ESCRTs. Certain accessory proteins have been implicated in regulating the activity or steady‐state expression levels of the ESCRT components, whereas other interactors control the cellular localization of the ESCRTs, for example, by inducing shuttling between cytosol and nucleus or endosomes. In conclusion, the discovery of novel interactors has and will extend our knowledge of the biological roles of ESCRTs.     

Protein-protein interactions of ESCRT complexes in the yeast Saccharomyces cerevisiae

Ten class E Vps proteins in yeast are known components of the ESCRT complexes I, II and III, which are required for the sorting of proteins to the lumenal membranes of multivesicular bodies. We used the yeast 2 hybrid system to analyze the protein–protein interactions of all 17 soluble class E Vps proteins, as well as proteins thought to be required for the ubiquitination and deubiquitination of cargo proteins at multivesicular bodies. We identified novel interactions between yeast ESCRT complex components suggesting that ESCRTI binds to both ESCRTII and ESCRTIII. These interactions were confirmed by GST pull-down experiments. Our data indicate that the link between ESCRTI and ESCRTIII is via Vps28p and Vps37p/Srn2p binding directly to Vps20p, as well as through indirect interactions via ESCRTII. This is in contrast to the situation in mammalian cells where ESCRTI and ESCRTIII interact indirectly via ALIX, the mammalian homologue of yeast proteins Vps31p/Bro1p and Rim20p. Our data also enable us to link all soluble class E Vps proteins to the ESCRT complexes. We propose the formation of a large multimeric complex on the endosome membrane consisting of ESCRTI, ESCRTII, ESCRTIII and other associated proteins.     

Evolution of the multivesicular body ESCRT machinery; retention across the eukaryotic lineage

Lysosomal targeting of ubiquitylated endocytic cargo is mediated in part by the endosomal sorting complex required for transport (ESCRT) complexes, a system conserved between animals and fungi (Opisthokonta). Extensive comparative genomic analysis demonstrates that ESCRT factors are well conserved across the eukaryotic lineage and complexes I, II, III and III-associated are almost completely retained, indicating an early evolutionary origin. The conspicuous exception is ESCRT 0, which functions in recognition of ubiquitylated cargo, and is restricted to the Opisthokonta, suggesting that a distinct mechanism likely operates in the vast majority of eukaryotic organisms. Additional analysis suggests that ESCRT III and ESCRT III-associated components evolved through a concerted model. Functional conservation of the ESCRT system is confirmed by direct study in trypanosomes. Despite extreme sequence divergence, epitope-tagged ESCRT factors TbVps23 and TbVps28 localize to the endosomal pathway, placing the trypanosome multivesicular body (MVB) in juxtaposition to the early endosome and lysosome. Knockdown of TbVps23 partially prevents degradation of an ubiquitylated endocytosed transmembrane domain protein. Therefore, despite the absence of an ESCRT 0 complex, the trypanosome ESCRT/MVB system functions similarly to that of opisthokonts. Thus the ESCRT system is an ancient and well-conserved feature of eukaryotic cells but with key differences between diverse lineages.     

ESCRT machinery and cytokinesis: the road to daughter cell separation

The endosomal sorting complex required for transport (ESCRT) machinery is a set of cellular protein complexes required for at least three topologically equivalent membrane scission events, namely multivesicular body (MVB) formation, retroviral particle release and midbody abscission during cytokinesis. Recently, several studies have explored the mechanism by which the core ESCRT-III subunits mediate membrane scission and might be differentially required according to the functions of the pathway. In this review, we discuss the links between the ESCRT machinery and cytokinesis, with special focus on abscission initiation and regulation.     

Structure/function analysis of four core ESCRT-III proteins reveals common regulatory role for extreme C-terminal domain

Endosomal sorting complex required for transport-III (ESCRT-III) is a large complex built from related ESCRT-III proteins involved in multivesicular body biogenesis. Little is known about the structure and function of this complex. Here, we compare four human ESCRT-III proteins - hVps2-1/CHMP2a, hVps24/CHMP3, hVps20/CHMP6, and hSnf7-1/CHMP4a - to each other, studying the effects of deleting predicted alpha-helical domains on their behavior in transfected cells. Surprisingly, removing approximately 40 amino acids from the C-terminus of each protein unmasks a common ability to associate with endosomal membranes and assemble into large polymeric complexes. Expressing these truncated ESCRT-III proteins in cultured cells causes ubiquitinated cargo to accumulate on enlarged endosomes and inhibits viral budding, while expressing full-length proteins does not. hVps2-1/CHMP2a lacking its C-terminal 42 amino acids further fails to bind to the AAA+ adenosine triphosphatase VPS4B/SKD1, indicating that C-terminal sequences are important for interaction of ESCRT-III proteins with VPS4. Overall, our study supports a model in which ESCRT-III proteins cycle between a default 'closed' state and an activated 'open' state under control of sequences at their C-terminus and associated factors.