Institute for Molecular Biophysics, Florida State University, Tallahassee, FL 32306-4380, USA.
J Struct Biol. 2011 Feb;173(2):358-64. doi: 10.1016/j.jsb.2010.09.002. Epub 2010 Sep 7.
Nearly a third of all eukaryotic proteins are transported from the ER to the Golgi apparatus through the secretory pathway using COPII coated vesicles. Evidence suggests that this transport occurs via 500-900 Å vesicles that bud from the ER membrane. It has been shown that procollagen molecules utilize the COPII proteins for transport, but it is unclear how the COPII coat can accommodate these ∼3000 Å long molecules. We now present a cryogenic electron tomographic reconstruction of a Sec13/31 tubule that is approximately 3300 Å long containing a hollow cylindrical interior that is 300 Å in diameter, dimensions that are consistent with those that are required to encapsulate a procollagen molecule wrapped in a membrane and accessory COPII components. This structure suggests a novel mechanism that the COPII coat may employ to transport elongated cargo.
近三分之一的真核生物蛋白通过 COPII 被膜小泡从内质网运输到高尔基体，通过分泌途径。有证据表明，这种运输是通过从内质网膜出芽的 500-900Å 的小泡进行的。已经表明原胶原分子利用 COPII 蛋白进行运输，但尚不清楚 COPII 外壳如何适应这些约 3000Å 长的分子。我们现在展示了一个约 3300Å 长的 Sec13/31 管的低温电子断层重建，其中包含一个直径为 300Å 的空心圆柱形内部，这些尺寸与包裹在膜中的原胶原分子和辅助 COPII 成分所需的尺寸一致。这种结构表明了一种新的机制，即 COPII 外壳可能用于运输伸长的货物。
