Ballesteros M L, Sánchez C M, Enjuanes L
Department of Molecular and Cell Biology, Campus Universidad Autónoma,Cantoblanco, Madrid, Spain.
Virology. 1997 Jan 20;227(2):378-88. doi: 10.1006/viro.1996.8344.
To study the molecular basis of TGEV tropism, a collection of recombinants between the PUR46-MAD strain of transmissible gastroenteritis coronavirus (TGEV) infecting the enteric and respiratory tracts and the PTV strain, which only infects the respiratory tract, was generated. The recombinant isolation frequency was about 10(-9) recombinants per nucleotide and was 3.7-fold higher at the 5'-end of the S gene than in other areas of the genome. Thirty recombinants were plaque purified and characterized phenotypically and genetically. All recombinant viruses had a single crossover and had inherited the 5'- and 3'-halves of their genome from the enteric and respiratory parents, respectively. Recombinant viruses were classified into three groups, named 1 to 3, according to the location of the crossover. Group 1 recombinants had the crossover in the S gene, while in Groups 2 and 3 the crossovers were located in ORF1b and ORF1a, respectively. The tropism of the recombinants was studied. Recombinants of Group 1 had enteric and respiratory tropism, while Group 2 recombinants infected the respiratory, but not the enteric, tract. Viruses of both groups differed by two nucleotide changes at positions 214 and 655. Both changes may be in principle responsible for the loss of enteric tropism but only the change in nucleotide 655 was specifically found in the respiratory isolates and most likely this single nucleotide change, which leads to a substitution in amino acid 219 of the S protein, was responsible for the loss of enteric tropism in the closely related PUR46 isolates. The available data indicate that in order to infect enteric tract cells with TGEV, two different domains of the S protein, mapping between amino acids 522 and 744 and around amino acid 219, respectively, are involved. The first domain binds to porcine aminopeptidase N, the cellular receptor for TGEV. In the other domain maps a second factor of undefined nature but which may be the binding site for a coreceptor essential for the enteric tropism of TGEV.
为研究猪传染性胃肠炎病毒（TGEV）嗜性的分子基础，构建了感染肠道和呼吸道的TGEV PUR46-MAD株与仅感染呼吸道的PTV株之间的一系列重组体。重组体的分离频率约为每核苷酸10^(-9)个重组体，在S基因的5'端比基因组的其他区域高3.7倍。对30个重组体进行了噬斑纯化，并进行了表型和遗传特征分析。所有重组病毒都有一个单交换，并分别从肠道亲本和呼吸道亲本继承了其基因组的5'端和3'端。根据交换位点的位置，重组病毒被分为三组，命名为1至3组。第1组重组体在S基因中有交换，而第2组和第3组的交换分别位于ORF1b和ORF1a中。研究了重组体的嗜性。第1组重组体具有肠道和呼吸道嗜性，而第2组重组体感染呼吸道，但不感染肠道。两组病毒在第214位和第655位有两个核苷酸变化。这两个变化原则上都可能导致肠道嗜性的丧失，但只有第655位的核苷酸变化在呼吸道分离株中被特异性发现，很可能是这个单核苷酸变化导致S蛋白第219位氨基酸的替换，从而导致密切相关的PUR46分离株肠道嗜性的丧失。现有数据表明，为了使TGEV感染肠道细胞，S蛋白的两个不同结构域分别位于氨基酸522至744之间和氨基酸219周围。第一个结构域与TGEV的细胞受体猪氨肽酶N结合。在另一个结构域中映射了一个性质未明的第二个因子，但它可能是TGEV肠道嗜性所必需的共受体的结合位点。
