Liao S, Lin J, Do H, Johnson A E
Department of Medical Biochemistry and Genetics, Texas A&M University Health Science Center, College Station 77843-1114, USA.
Cell. 1997 Jul 11;90(1):31-41. doi: 10.1016/s0092-8674(00)80311-6.
Portions of the nascent chain are exposed to the lumen, the cytosol, or neither at different stages during the cotranslational integration of a protein into the ER membrane, as shown by compartment-specific collisional quenching of fluorophores incorporated into the polypeptide. The opening or closing of each end of the aqueous translocon pore is tightly controlled and occurs in a sequence that does not compromise the membrane's permeability barrier. Surprisingly, these structural changes at the membrane are effected by the transmembrane segment in the nascent protein from inside the ribosome. Thus, the ribosome, not the translocon, first recognizes the transmembrane segment and triggers long-range structural changes at the translocon that may be involved in shifting its function from translocation to integration.
在蛋白质共翻译整合到内质网（ER）膜的不同阶段，新生肽链的部分区域会暴露于内质网腔、细胞质溶胶中，或者都不暴露，这是通过掺入多肽中的荧光团在特定区域的碰撞猝灭来证明的。水性转运体孔两端的打开或关闭受到严格控制，且按不损害膜通透性屏障的顺序发生。令人惊讶的是，膜上的这些结构变化是由核糖体内部新生蛋白质中的跨膜片段引起的。因此，首先识别跨膜片段并触发转运体上远距离结构变化的是核糖体，而非转运体，这些结构变化可能涉及将转运体的功能从转运转变为整合。
