Morrison T, McQuain C, Sergel T, McGinnes L, Reitter J
Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester 01655.
Virology. 1993 Apr;193(2):997-1000. doi: 10.1006/viro.1993.1214.
Phenylalanine is the amino acid at the amino terminus of the F1 protein of all paramyxovirus fusion proteins with the exception of the avirulent strains of Newcastle disease virus, which have a leucine residue in this position (Toyoda et al. (1989) Virology 169, 273-282). To explore the role of this phenylalanine in the fusion activity of the protein, this residue, amino acid 117 in the fusion protein sequence, was changed to leucine (F117L) or to glycine (F117G) by site-specific mutagenesis while maintaining the cleavage site sequence of virulent strains of NDV. While both wild-type and the F117G protein were proteolytically cleaved and F1 was detected, the F117L protein was not cleaved. In the presence of the HN protein, both wild-type F and F117G proteins stimulated fusion, but the F117L protein was inactive in fusion. However, incubation in trypsin activated the fusion activity of the protein. Thus the phenylalanine at the amino terminus of the F1 component of the fusion protein is not required for the fusion activity of the protein. The presence of a leucine at this position blocks cleavage even though the cleavage site sequence is unchanged.
除了新城疫病毒无毒株外，所有副粘病毒融合蛋白F1蛋白的氨基末端氨基酸均为苯丙氨酸，新城疫病毒无毒株在该位置有一个亮氨酸残基（丰田等人，（1989年）《病毒学》169，273 - 282）。为了探究该苯丙氨酸在蛋白融合活性中的作用，通过定点诱变将融合蛋白序列中第117位氨基酸残基（即该苯丙氨酸）替换为亮氨酸（F117L）或甘氨酸（F117G），同时保持新城疫病毒强毒株的裂解位点序列。虽然野生型和F117G蛋白都能被蛋白酶裂解并检测到F1，但F117L蛋白未被裂解。在HN蛋白存在的情况下，野生型F蛋白和F117G蛋白都能刺激融合，但F117L蛋白在融合方面无活性。然而，用胰蛋白酶孵育可激活该蛋白的融合活性。因此，融合蛋白F1组分氨基末端的苯丙氨酸对于该蛋白的融合活性并非必需。即使裂解位点序列未改变，该位置存在亮氨酸也会阻止裂解。
