Dierks T, Klappa P, Wiech H, Zimmermann R
Zentrum Biochemie/Abteilung Biochemie II der Universität, F.R.G.
Philos Trans R Soc Lond B Biol Sci. 1993 Mar 29;339(1289):335-41. doi: 10.1098/rstb.1993.0032.
In eukaryotic cells export of the vast majority of newly synthesized secretory proteins is initiated at the level of the membrane of the endoplasmic reticulum (microsomal membrane). The precursors of secretory proteins are not transported across the microsomal membrane in their native state. Typically, signal peptides in the precursor proteins are involved in preserving the transport-competent state. Furthermore, there are two alternatively acting mechanisms involved in preserving transport competence in the cytosol. The first mechanism involves two ribonucleoparticles (ribosome and signal recognition particle) and their receptors on the microsomal surface and requires the hydrolysis of GTP. The second mechanism does not involve ribonucleoparticles and their receptors but depends on the hydrolysis of ATP and on cis-acting molecular chaperones, such as heat shock cognate protein 70 (hsc 70). In both mechanisms a translocase in the microsomal membrane mediates protein translocation. This translocase includes a signal peptide receptor on the cis-side of the microsomal membrane and a component that also depends on the hydrolysis of ATP. At least in certain cases, an additional nucleoside triphosphate-requiring step is involved which is related to the trans-acting molecular chaperone BiP.
在真核细胞中，绝大多数新合成的分泌蛋白的输出始于内质网（微粒体膜）膜水平。分泌蛋白的前体并非以其天然状态跨微粒体膜转运。通常，前体蛋白中的信号肽参与维持可转运状态。此外，在细胞质溶胶中存在两种交替起作用的机制来维持转运能力。第一种机制涉及两个核糖核蛋白颗粒（核糖体和信号识别颗粒）及其在微粒体表面的受体，并且需要GTP水解。第二种机制不涉及核糖核蛋白颗粒及其受体，但依赖于ATP水解和顺式作用分子伴侣，如热休克同源蛋白70（hsc 70）。在这两种机制中，微粒体膜中的转位酶介导蛋白质转位。这种转位酶包括微粒体膜顺式侧的信号肽受体和一个也依赖于ATP水解的组分。至少在某些情况下，涉及一个额外的需要核苷三磷酸的步骤，这与反式作用分子伴侣BiP有关。
