Filoviridae. Filoviridae

Description of Filoviridae adapted from ICTVdb Virion Properties Morphology Virions consist of an envelope, a nucleocapsid, a polymerase complex, and a matrix protein. Virus capsid is enveloped. Virions are filamentous, or pleomorphic, flexible with extensive branching. U- or 6-shaped and circular forms occur particularly after purification. Virions measure about 80 nm in diameter; greatly variable up to 1400 nm in length, or 790-970 nm in length (after purification). Surface projections are spaced widely apart, distinctive knob-shaped peplomers that cover evenly the surface and are embedded in a lipid bilayer. Surface projections are composed of one type of glycoproteins (GP), are 10 nm long and spaced 10 nm apart. Capsid/nucleocapsid is elongated and exhibits helical symmetry. The nucleocapsid is helical; is cross-striated and a width of 50 nm. Axial canal is distinct and 20 nm in diameter. Basic helix is obvious. Pitch of helix is 5 nm. Physicochemical and Physical Properties The molecular mass (Mr) of virions is 382 x 106. Virions have a buoyant density in CsCl of 1.32 g cm-3 (for nucleocapsids). The density of virions is 1.14 g cm-3 (in potassium tartrate gradient). The sedimentation coefficient is 1.4 S20w (for longer particles it is very high). The thermal inactivation point (TIP) is at about 60°C (after 30 min). Under in vitro conditions virions are relatively stable when stored at 15°C to 20°C; sensitivecanal is distinct; acid environment of pH 5 (hypochlorite, sensitivecanal is distinct; alkaline environment of pH 8 (quaternary ammonium salt). Virions are sensitive to treatment with lipid solvents, phenol (phenolic disinfectants), formaldehyde, and ß-propiolactone. The infectivity is reduced after exposure to irradiation (UV and gamma irradiation). Nucleic Acid The Mr of the genome constitutes 1.1% of the virion by weight. The genome is not segmented and contains a single molecule of linear negative-sense, single-stranded RNA. The complete genome is 18900-19000 nucleotides long. The RNA is sequenced, but only an estimate is available, complete sequence is 18900-19000 nucleotides long. Nucleotide sequences at the 3'-terminus are complementary to similar regions on the 5' end. The 5'-end of the negative-sense strand does not have a covalently attached terminal protein; genome does not have cap. The 3'-terminus has conserved nucleotide sequences (leader, in genera of same family. The 3'-terminus has no poly (A) tract. Proteins The viral genome encodes structural proteins and non-structural proteins. Virions consist of 5 structural protein(s) located in the envelope (surface glycoprotein), nucleocapsid (NP), polymerase complex (transcriptase-polymerase component and RNA-dependent RNA transcriptase-polymerase), matrix. Structural Proteins: Envelope protein GP has a molecular mass of 74500-74800 Da. Envelope protein has a function assigned; is a glycoprotein and forming the viral spikes (in the form of trimers, during post-translational processing envelope protein modifications occur that include glycosylation (of the first small ORF yielding a soluble small glycoprotein sGP, not observed in Marburg virus). Nucleocapsid protein NP has a molecular mass of 77900-83300 Da; is binding to the genomic RNA. Nucleocapsid protein VP30; has a molecular mass of 29700-31500 Da. Matrix protein VP40; has a molecular mass of 31700-35800 Da. Matrix protein is a transmembrane protein, or a membrane-associated protein. Matrix protein VP24; has a molecular mass of 28300-28800 Da. Matrix protein is presumably transmembrane protein, or membrane-associated protein. Lipids Lipids are present and located in the envelope. The composition of viral lipids and host cell membranes are similar. Genome Organization and Replication By itself, genomic nucleic acid is not infectious.

丝状病毒科（Filoviridae）的描述改编自国际病毒分类委员会数据库（ICTVdb）的病毒粒子特性章节。
### 形态学
病毒粒子由包膜、核衣壳（nucleocapsid）、聚合酶复合物（polymerase complex）与基质蛋白构成，病毒衣壳被包膜包裹。病毒粒子呈丝状或多形性，具有柔韧性且广泛分支；U形、6形及环状形态在纯化后尤为常见。病毒粒子直径约80 nm，长度变异范围极大，可达1400 nm；纯化后长度为790~970 nm。
病毒粒子表面突起间距较大，为特征性的 knob状包膜子粒（peplomer），均匀覆盖于病毒粒子表面并嵌入脂质双层。该表面突起由一种糖蛋白（GP）构成，长10 nm，间距为10 nm。
核衣壳呈拉长状，具有螺旋对称特征；螺旋形核衣壳具横纹，宽度为50 nm，轴道清晰，直径20 nm，基础螺旋明显，螺旋螺距为5 nm。

### 理化与物理特性
病毒粒子的分子质量（Mr）为382×10^6。核衣壳在氯化铯（CsCl）中的浮力密度为1.32 g·cm^-3；病毒粒子在酒石酸钾梯度中的密度为1.14 g·cm^-3。沉降系数为1.4 S20w（较长粒子的沉降系数极高）。热灭活点（TIP）约为60℃（处理30 min后）。
体外条件下，15℃~20℃储存时病毒粒子相对稳定；其对pH 5的酸性环境（次氯酸盐可灭活此类病毒）、pH 8的碱性环境（季铵盐类消毒剂可灭活此类病毒）敏感。病毒粒子对脂溶剂、苯酚（酚类消毒剂）、甲醛及β-丙内酯处理敏感。紫外线与γ射线照射可降低其感染性。

### 核酸
基因组的分子质量占病毒粒子总质量的1.1%。基因组不分节段，为单分子线性负链单链RNA。完整基因组长度为18900~19000核苷酸。该RNA已完成测序，但仅为估算值，完整序列长度为18900~19000核苷酸。3'端核苷酸序列与5'端的相似区域互补。负链的5'端无共价结合的末端蛋白；基因组无帽子结构。3'端具有保守核苷酸序列（先导序列，存在于同科各属中），且3'端无poly(A)尾。

### 蛋白质
病毒基因组编码结构蛋白与非结构蛋白。病毒粒子包含5种结构蛋白，分别定位于包膜（表面糖蛋白GP）、核衣壳（NP）、聚合酶复合物（转录酶-聚合酶组分与RNA依赖的RNA转录酶-聚合酶）以及基质中。
结构蛋白详情如下：
1. 包膜蛋白GP：分子质量为74500~74800 Da，功能已明确，为糖蛋白，以三聚体形式构成病毒刺突；翻译后修饰过程中，包膜蛋白会发生糖基化修饰（首个小开放阅读框（ORF）可编码可溶性小糖蛋白sGP，但马尔堡病毒未观察到此现象）。
2. 核衣壳蛋白NP：分子质量为77900~83300 Da，可与基因组RNA结合。
3. 核衣壳蛋白VP30：分子质量为29700~31500 Da。
4. 基质蛋白VP40：分子质量为31700~35800 Da，属于跨膜蛋白或膜相关蛋白。
5. 基质蛋白VP24：分子质量为28300~28800 Da，推测为跨膜蛋白或膜相关蛋白。

### 脂质
脂质存在于病毒包膜中，其组成与宿主细胞膜相似。

### 基因组组织与复制
单独的基因组核酸不具有感染性。