Identification of Domains on the Fusion (F) Protein Trimer That Influence the Hemagglutinin-Neuraminidase Specificity of the F Protein in Mediating Cell-Cell Fusion

For most paramyxoviruses, virus type-specific interaction between fusion (F) protein and attachment protein (hemagglutinin-neuraminidase [HN], hemagglutinin [H], or glycoprotein [G]) is a prerequisite for mediating virus-cell fusion and cell-cell fusion. Our previous cell-cell fusion assay using the chimeric F proteins of human parainfluenza virus 2 (HPIV2) and simian virus 41 (SV41) suggested that the middle region of the HPIV2 F protein contains the site(s) that determines its specificity for the HPIV2 HN protein. In the present study, we further investigated the sites of the F protein that could be critical for determining the HN protein specificity. By analyzing the reported structure of the F protein of parainfluenza virus 5 (PIV5), we found that four major domains (M1, M2, M3, and M4) and five minor domains (A to E) in the middle region of the PIV5 F protein were exposed on the trimer surface. We then replaced these domains with the SV41 F counterparts individually or in combination and examined whether the resulting chimeras could mediate cell-cell fusion when coexpressed with the SV41 HN protein. The results showed that a chimera designated M(1 + 2), which harbored SV41 F-derived domains M1 and M2, mediated cell-cell fusion with the coexpressed SV41 HN protein, suggesting that these domains are involved in determining the HN protein specificity. Intriguingly, another chimera which harbored the SV41 F-derived domain B in addition to domains M1 and M2 showed increased specificity for the SV41 HN protein compared to that of M(1 + 2), although it was capable of mediating cell-cell fusion by itself.

对于大多数副粘病毒而言，融合蛋白（F）和附着蛋白（血凝素 - 神经氨酸酶[HN]、血凝素[H]或糖蛋白[G]）之间的病毒类型特异性相互作用是介导病毒 - 细胞融合以及细胞 - 细胞融合的先决条件。我们之前利用人副流感病毒2（HPIV2）和猴病毒41（SV41）的嵌合F蛋白进行的细胞 - 细胞融合试验表明，HPIV2 F蛋白的中间区域包含决定其对HPIV2 HN蛋白特异性的位点。在本研究中，我们进一步探究了F蛋白中对决定HN蛋白特异性可能至关重要的位点。通过分析已报道的副流感病毒5（PIV5）F蛋白的结构，我们发现PIV5 F蛋白中间区域的四个主要结构域（M1、M2、M3和M4）以及五个次要结构域（A到E）暴露在三聚体表面。然后我们将这些结构域单独或组合地用SV41 F蛋白的相应部分替换，并检测当与SV41 HN蛋白共表达时，所得的嵌合体是否能够介导细胞 - 细胞融合。结果显示，一种名为M(1 + 2)的嵌合体，其包含源自SV41 F的结构域M1和M2，能够与共表达的SV41 HN蛋白介导细胞 - 细胞融合，这表明这些结构域参与决定HN蛋白的特异性。有趣的是，另一种除了结构域M1和M2之外还包含源自SV41 F的结构域B的嵌合体，与M(1 + 2)相比，对SV41 HN蛋白表现出更高的特异性，尽管它自身能够介导细胞 - 细胞融合。