Department of Biochemistry, University of Washington, Seattle, Washington, USA.
Institut Pasteur, Unité de Virologie Structurale, Paris, France.
J Virol. 2018 Jan 30;92(4). doi: 10.1128/JVI.01628-17. Print 2018 Feb 15.
Coronaviruses recently emerged as major human pathogens causing outbreaks of severe acute respiratory syndrome and Middle East respiratory syndrome. They utilize the spike (S) glycoprotein anchored in the viral envelope to mediate host attachment and fusion of the viral and cellular membranes to initiate infection. The S protein is a major determinant of the zoonotic potential of coronaviruses and is also the main target of the host humoral immune response. We report here the 3.5-Å-resolution cryo-electron microscopy structure of the S glycoprotein trimer from the pathogenic porcine deltacoronavirus (PDCoV), which belongs to the recently identified genus. Structural and glycoproteomics data indicate that the glycans of PDCoV S are topologically conserved compared with the human respiratory coronavirus NL63 S, resulting in similar surface areas being shielded from neutralizing antibodies and implying that both viruses are under comparable immune pressure in their respective hosts. The structure further reveals a shortened S' activation loop, containing a reduced number of basic amino acids, which participates in rendering the spike largely protease resistant. This property distinguishes PDCoV S from recently characterized betacoronavirus S proteins and suggests that the S protein of enterotropic PDCoV has evolved to tolerate the protease-rich environment of the small intestine and to fine-tune its fusion activation to avoid premature triggering and reduction of infectivity. Coronaviruses use transmembrane S glycoprotein trimers to promote host attachment and fusion of the viral and cellular membranes. We determined a near-atomic-resolution cryo-electron microscopy structure of the S ectodomain trimer from the pathogenic PDCoV, which is responsible for diarrhea in piglets and has had devastating consequences for the swine industry worldwide. Structural and glycoproteomics data reveal that PDCoV S is decorated with 78 N-linked glycans obstructing the protein surface to limit accessibility to neutralizing antibodies in a way reminiscent of what has recently been described for a human respiratory coronavirus. PDCoV S is largely protease resistant, which distinguishes it from most other characterized coronavirus S glycoproteins and suggests that enteric coronaviruses have evolved to fine-tune fusion activation in the protease-rich environment of the small intestine of infected hosts.
冠状病毒最近成为导致严重急性呼吸系统综合征和中东呼吸系统综合征爆发的主要人类病原体。它们利用锚定在病毒包膜中的刺突（S）糖蛋白介导宿主附着和病毒与细胞膜的融合，从而引发感染。S 蛋白是冠状病毒人畜共患病潜力的主要决定因素，也是宿主体液免疫反应的主要目标。我们在此报告致病性猪德尔塔冠状病毒（PDCoV）S 糖蛋白三聚体的 3.5 Å 分辨率冷冻电镜结构，该病毒属于最近确定的属。结构和糖蛋白组学数据表明，与人类呼吸道冠状病毒 NL63 S 相比，PDCoV S 的聚糖在拓扑上是保守的，导致相似的表面区域被中和抗体屏蔽，这意味着这两种病毒在各自的宿主中受到类似的免疫压力。该结构进一步揭示了一个缩短的 S'激活环，其中包含较少数量的碱性氨基酸，这有助于使刺突蛋白在很大程度上抵抗蛋白酶。这一特性将 PDCoV S 与最近鉴定的β冠状病毒 S 蛋白区分开来，并表明肠致病性 PDCoV 的 S 蛋白已经进化为耐受小肠中富含蛋白酶的环境，并精细调节其融合激活，以避免过早触发和降低感染力。冠状病毒使用跨膜 S 糖蛋白三聚体促进宿主附着和病毒与细胞膜的融合。我们确定了致病性 PDCoV 的 S 外域三聚体的近原子分辨率冷冻电镜结构，该结构负责仔猪腹泻，对全球养猪业造成了毁灭性的后果。结构和糖蛋白组学数据表明，PDCoV S 被 78 个 N 连接聚糖修饰，这些聚糖阻碍了蛋白质表面，以限制中和抗体的可及性，这种方式类似于最近描述的人类呼吸道冠状病毒。PDCoV S 具有很强的抗蛋白酶性，这将其与大多数其他已鉴定的冠状病毒 S 糖蛋白区分开来，并表明肠冠状病毒已经进化为在感染宿主的小肠富含蛋白酶的环境中精细调节融合激活。
