Matlack K E, Misselwitz B, Plath K, Rapoport T A
Howard Hughes Medical Institute, Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115-6091, USA.
Cell. 1999 May 28;97(5):553-64. doi: 10.1016/s0092-8674(00)80767-9.
We have addressed the mechanism by which proteins are posttranslationally transported across the membrane of the yeast endoplasmic reticulum (ER). We demonstrate that BiP (Kar2p), a member of the Hsp70 family resident in the ER lumen, acts as a molecular ratchet during translocation of the secretory protein prepro-alpha factor through the channel formed by the Sec complex. Multiple BiP molecules associate with each translocation substrate following interaction with the J domain of the Sec63p component of the Sec complex. Bound BiP minimizes passive backward movements of the substrate through the channel, and BiP's subsequent dissociation results in a free polypeptide in the ER lumen. Antibodies against the substrate can replace BiP, indicating that a Brownian ratchet is sufficient to achieve translocation.
我们已经研究了蛋白质在翻译后跨酵母内质网（ER）膜转运的机制。我们证明，驻留在内质网腔中的Hsp70家族成员BiP（Kar2p）在分泌蛋白前原α因子通过Sec复合物形成的通道进行转运过程中充当分子棘轮。多个BiP分子在与Sec复合物的Sec63p组分的J结构域相互作用后与每个转运底物结合。结合的BiP使底物通过通道的被动向后移动最小化，并且BiP随后的解离导致内质网腔中的游离多肽。针对底物的抗体可以替代BiP，这表明布朗棘轮足以实现转运。
