Department of Structural Biology, Stanford Universitygrid.168010.egrid.471392.a School of Medicine, Stanford, California, USA.
Department of Molecular Microbiology & Immunology, Oregon Health & Science University, Portland, Oregon, USA.
mBio. 2021 Oct 26;12(5):e0262521. doi: 10.1128/mBio.02625-21.
Human cytomegalovirus (HCMV) is a herpesvirus that produces disease in transplant patients and newborn children. Entry of HCMV into cells relies on gH/gL trimer (gHgLgO) and pentamer (gHgLUL128-131) complexes that bind cellular receptors. Here, we studied the structure and interactions of the HCMV trimer, formed by AD169 strain gH and gL and TR strain gO proteins, with the human platelet-derived growth factor receptor alpha (PDGFRα). Three trimer surfaces make extensive contacts with three PDGFRα N-terminal domains, causing PDGFRα to wrap around gO in a structure similar to a human hand, explaining the high-affinity interaction. gO is among the least conserved HCMV proteins, with 8 distinct genotypes. We observed high conservation of residues mediating gO-gL interactions but more extensive gO variability in the PDGFRα interface. Comparisons between our trimer structure and a previously determined structure composed of different subunit genotypes indicate that gO variability is accommodated by adjustments in the gO-PDGFRα interface. We identified two loops within gO that were disordered and apparently glycosylated, which could be deleted without disrupting PDGFRα binding. We also identified four gO residues that contact PDGFRα, which when mutated produced markedly reduced receptor binding. These residues fall within conserved contact sites of gO with PDGFRα and may represent key targets for anti-trimer neutralizing antibodies and HCMV vaccines. Finally, we observe that gO mutations distant from the gL interaction site impact trimer expression, suggesting that the intrinsic folding or stability of gO can impact the efficiency of trimer assembly. HCMV is a herpesvirus that infects a large percentage of the adult population and causes significant levels of disease in immunocompromised individuals and birth defects in the developing fetus. The virus encodes a complex protein machinery that coordinates infection of different cell types in the body, including a trimer formed of gH, gL, and gO subunits. Here, we studied the interactions of the HCMV trimer with its receptor on cells, the platelet derived growth factor receptor α (PDGFRα), to better understand how HCMV coordinates virus entry into cells. Our results add to our understanding of HCMV strain-specific differences and identify sites on the trimer that represent potential targets for therapeutic antibodies or vaccine development.
人巨细胞病毒（HCMV）是一种疱疹病毒，可导致移植患者和新生儿患病。HCMV 进入细胞依赖于 gH/gL 三聚体（gHgLgO）和五聚体（gHgLUL128-131）复合物与细胞受体结合。在这里，我们研究了 AD169 株 gH 和 gL 与 TR 株 gO 蛋白形成的 HCMV 三聚体的结构和相互作用，与人类血小板衍生生长因子受体α（PDGFRα）。三个三聚体表面与三个 PDGFRα N 端结构域广泛接触，导致 PDGFRα 在 gO 周围形成类似于人手的结构，解释了高亲和力相互作用。gO 是 HCMV 中最不保守的蛋白质之一，有 8 种不同的基因型。我们观察到介导 gO-gL 相互作用的残基高度保守，但 PDGFRα 界面的 gO 可变性更大。我们的三聚体结构与先前由不同亚基基因型组成的结构进行比较表明，gO 的可变性可以通过调整 gO-PDGFRα 界面来适应。我们确定了 gO 内两个无规卷曲且显然糖基化的环，这些环缺失不会破坏 PDGFRα 结合。我们还鉴定了四个与 PDGFRα 相互作用的 gO 残基，当这些残基发生突变时，受体结合明显减少。这些残基位于 gO 与 PDGFRα 的保守接触位点内，可能是抗三聚体中和抗体和 HCMV 疫苗的关键靶点。最后，我们观察到 gO 远离 gL 相互作用位点的突变会影响三聚体的表达，这表明 gO 的固有折叠或稳定性会影响三聚体组装的效率。HCMV 是一种疱疹病毒，感染了很大一部分成年人，并导致免疫功能低下的个体和发育中胎儿的出生缺陷。该病毒编码了一种复杂的蛋白质机制，协调了体内不同类型细胞的感染，包括由 gH、gL 和 gO 亚基组成的三聚体。在这里，我们研究了 HCMV 三聚体与细胞上其受体血小板衍生生长因子受体α（PDGFRα）的相互作用，以更好地了解 HCMV 如何协调病毒进入细胞。我们的研究结果增加了对 HCMV 株特异性差异的理解，并确定了三聚体上可能作为治疗性抗体或疫苗开发的潜在靶点。
