Prange R, Streeck R E
Institute for Medical Microbiology, Johannes Gutenberg-Universität-Mainz, Germany.
EMBO J. 1995 Jan 16;14(2):247-56. doi: 10.1002/j.1460-2075.1995.tb06998.x.
The small (S), middle (M) and large (L) envelope proteins of the hepatitis B virus (HBV) are initially synthesized as multispanning membrane proteins of the endoplasmic reticulum membrane. We now demonstrate that all envelope proteins synthesized in transfected cells or in a cell-free system adopt more than one transmembrane orientation. The L protein disposes its N-terminal preS domain both to the cytoplasmic and the luminal side of the membrane. This unusual topology does not depend on interaction with the viral nucleocapsid, but is preserved in secreted empty envelope particles. Pulse-chase analysis suggests a novel process of post-translational translocation leading to the non-uniform topology. Analysis of L deletion mutants indicates that the block to co-translational translocation can be attributed to a specific sequence within preS, suggesting that translocation of L may be regulated. Additional topological heterogeneity is displayed in the S region of the envelope proteins and in the S protein itself, as assayed in a cell-free system. S proteins integrated into microsomal membranes exhibit both a luminal and a cytoplasmic orientation of the internal hydrophilic region carrying the major antigenic determinants. This may explain the unusual partial glycosylation of the HBV envelope proteins.
乙型肝炎病毒（HBV）的小（S）、中（M）和大（L）包膜蛋白最初作为内质网膜的多跨膜蛋白合成。我们现在证明，在转染细胞或无细胞系统中合成的所有包膜蛋白都采用不止一种跨膜方向。L蛋白将其N端前S结构域置于膜的细胞质侧和腔侧。这种不寻常的拓扑结构不依赖于与病毒核衣壳的相互作用，而是保留在分泌的空包膜颗粒中。脉冲追踪分析表明，存在一种导致非均匀拓扑结构的新型翻译后易位过程。对L缺失突变体的分析表明，共翻译易位的阻断可归因于前S内的特定序列，这表明L的易位可能受到调控。如在无细胞系统中检测到的那样，包膜蛋白的S区域和S蛋白本身还表现出额外的拓扑异质性。整合到微粒体膜中的S蛋白在携带主要抗原决定簇的内部亲水区域表现出腔侧和细胞质侧方向。这可能解释了HBV包膜蛋白不寻常的部分糖基化现象。
