Werr M, Prange R
Institute for Medical Microbiology and Hygiene, Johannes Gutenberg-Universität Mainz, Germany.
J Virol. 1998 Jan;72(1):778-82. doi: 10.1128/JVI.72.1.778-782.1998.
Unlike those of the S and the L envelope proteins, the functional role of the related M protein in the life cycle of the hepatitis B virus (HBV) is less understood. We now demonstrate that a single N glycan, specific for M, is required for efficient secretion of M empty envelope particles. Moreover, this glycan mediates specific association of M with the chaperone calnexin. Conversely, the N glycan, common to all three envelope proteins, is involved neither in calnexin binding nor in subviral particle release. As proper folding and trafficking of M need the assistance of the chaperone, the glycan-dependent association of M with calnexin may thus play a crucial role in the assembly of HBV. Beyond being modified by N glycosylation, M is modified by O glycosylation occurring within its amino acid sequence at positions 27 to 47. The O glycans, however, were found to be dispensable for secretion of M but may rather support viral infectivity. Surprisingly, nonglycosylated M localizes exclusively to the cytosol, either for degradation or for a yet-unknown function.
与S包膜蛋白和L包膜蛋白不同，人们对相关M蛋白在乙型肝炎病毒（HBV）生命周期中的功能作用了解较少。我们现在证明，M蛋白特有的单个N聚糖是M空包膜颗粒有效分泌所必需的。此外，这种聚糖介导M蛋白与伴侣蛋白钙连蛋白的特异性结合。相反，所有三种包膜蛋白共有的N聚糖既不参与钙连蛋白结合，也不参与亚病毒颗粒释放。由于M蛋白的正确折叠和运输需要伴侣蛋白的协助，因此M蛋白与钙连蛋白的聚糖依赖性结合可能在HBV组装中起关键作用。除了进行N糖基化修饰外，M蛋白还在其氨基酸序列中第27至47位发生O糖基化修饰。然而，发现O聚糖对于M蛋白的分泌是可有可无的，但可能有助于病毒感染性。令人惊讶的是，非糖基化的M蛋白仅定位于细胞质中，要么用于降解，要么用于一种尚不清楚的功能。
