Leser G P, Ector K J, Ng D T, Shaughnessy M A, Lamb R A
Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208-3500, USA.
Virology. 1999 Sep 15;262(1):79-92. doi: 10.1006/viro.1999.9890.
The hemagglutinin-neuraminidase (HN) glycoprotein of the paramyxovirus SV5 is internalized from the cell surface via clathrin-coated pits. However, the cytoplasmic domain of SV5 HN does not contain a previously characterized internalization motif. A cell-surface-expressed chimeric protein (APK), consisting of the cytoplasmic tail, transmembrane (TM) domain, and 12 residues of the ectodomain of HN joined to the cytoplasmic protein pyruvate kinase is internalized, indicating that the N-terminal region of HN contains an internalization signal. Although SV5 HN is internalized at a rate similar to that of influenza virus hemagglutinin (HA) mutant Y543, which contains a degenerate tyrosine-based signal in its cytoplasmic tail, the elimination of the majority of the HN cytoplasmic tail, or substitution of the HN TM domain with leucine residues, did not affect the rate of HN internalization. The HN protein of the closely related virus, Newcastle disease virus (NDV), is not internalized from the cell surface. Working under the usual convention that the TM domain consists of the hydrophobic residues bounded by two charged residues, analysis of internalization of mutant and chimeric NDV HN molecules indicates that the first seven SV5 HN ectodomain residues are critical for internalization of HN. A glutamic acid residue (E37) that abuts this presumptive HN TM domain/ectodomain boundary is important for SV5 HN internalization.
副粘病毒SV5的血凝素神经氨酸酶（HN）糖蛋白通过网格蛋白包被小窝从细胞表面内化。然而，SV5 HN的胞质结构域并不包含先前已鉴定的内化基序。一种细胞表面表达的嵌合蛋白（APK），由HN的胞质尾、跨膜（TM）结构域以及胞外结构域的12个残基与胞质蛋白丙酮酸激酶连接而成，它能够被内化，这表明HN的N端区域含有一个内化信号。尽管SV5 HN的内化速率与流感病毒血凝素（HA）突变体Y543相似，后者在其胞质尾中含有一个简并的基于酪氨酸的信号，但去除大部分HN胞质尾，或将HN的TM结构域用亮氨酸残基替代，均不影响HN的内化速率。密切相关的病毒新城疫病毒（NDV）的HN蛋白不会从细胞表面内化。按照通常的惯例，TM结构域由两个带电荷残基界定的疏水残基组成，对突变体和嵌合NDV HN分子的内化分析表明，SV5 HN胞外结构域的前七个残基对HN的内化至关重要。紧邻这个假定的HN TM结构域/胞外结构域边界的一个谷氨酸残基（E37）对SV5 HN的内化很重要。
