Center for Integrated Protein Science Munich at the Department of Chemistry, Technical University of Munich, Garching, Germany.
Physical Chemistry, Department of Chemistry, Munich Center for Integrated Protein Science, Nanosystems Initiative Munich and Center for Nanoscience, Ludwig Maximilians University of Munich, Munich, Germany.
Nat Struct Mol Biol. 2018 Jan;25(1):90-100. doi: 10.1038/s41594-017-0012-6. Epub 2018 Jan 1.
BiP is the endoplasmic member of the Hsp70 family. BiP is regulated by several co-chaperones including the nucleotide-exchange factor (NEF) Bap (Sil1 in yeast). Bap is a two-domain protein. The interaction of the Bap C-terminal domain with the BiP ATPase domain is sufficient for its weak NEF activity. However, stimulation of the BiP ATPase activity requires full-length Bap, suggesting a complex interplay of these two factors. Here, single-molecule FRET experiments with mammalian proteins reveal that Bap affects the conformation of both BiP domains, including the lid subdomain, which is important for substrate binding. The largely unstructured Bap N-terminal domain promotes the substrate release from BiP. Thus, Bap is a conformational regulator affecting both nucleotide and substrate interactions. The preferential interaction with BiP in its ADP state places Bap at a late stage of the chaperone cycle, in which it coordinates release of substrate and ADP, thereby resetting BiP for ATP and substrate binding.
BIP 是 Hsp70 家族的内质成员。BIP 受几种共伴侣调节，包括核苷酸交换因子（NEF）Bap（酵母中的 Sil1）。Bap 是一种具有两个结构域的蛋白质。Bap C 末端结构域与 BIP ATP 酶结构域的相互作用足以使其具有较弱的 NEF 活性。然而，BIP ATP 酶活性的刺激需要全长 Bap，这表明这两个因素之间存在复杂的相互作用。在这里，使用哺乳动物蛋白的单分子 FRET 实验表明，Bap 影响两个 BIP 结构域的构象，包括对底物结合很重要的盖亚结构域。Bap 的无结构 N 末端结构域促进了底物从 BIP 的释放。因此，Bap 是一种构象调节剂，影响核苷酸和底物相互作用。它在 ADP 状态下优先与 BIP 相互作用，使 Bap 处于伴侣周期的后期，在这个阶段，它协调底物和 ADP 的释放，从而重置 BIP 以结合 ATP 和底物。
