Structural analysis of the Sil1-Bip complex reveals the mechanism for Sil1 to function as a nucleotide-exchange factor.
Structural analysis of the Sil1-Bip complex reveals the mechanism for Sil1 to function as a nucleotide-exchange factor.
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DOI：
10.1042/bj20110500
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发表时间：
2011-09
期刊：
影响因子：
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通讯作者：
M. Yan;Jingzhi Li;B. Sha
中科院分区：
文献类型：
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作者：
M. Yan;Jingzhi Li;B. Sha
Sil1在真核细胞中是内质网Hsp70(70 kDa热休克蛋白)Bip的核苷酸交换因子。Sil1可能通过直接与Bip的ATPase结构域相互作用来催化Bip释放ADP。在本研究中，我们展示了酵母Bip和NEF Sil1的复杂晶体结构，分辨率为2.3？(1？=0.1 nm)。在Sil1-Bip复合体结构中，Sil1分子起到了结合Bip ATPase结构域的叶IIb的‘钳’的作用。Sil1的结合导致叶IIb旋转~13.5°，远离ADP结合口袋。这种复杂的形成还导致叶Ib向相反方向摆动约3.7°。这些构象变化打开了Bip ATPase结构域中的核苷酸结合口袋，破坏了Bip与结合的ADP之间的氢键，从而可能催化ADP的释放。参与Bip ATPase结构域结合的Sil1残基的突变损害了Sil1与Bip的结合亲和力，并且这些Sil1突变也取消了刺激Bip ATPase活性的能力。
Sil1 functions as a NEF (nucleotide-exchange factor) for the ER (endoplasmic reticulum) Hsp70 (heat-shock protein of 70 kDa) Bip in eukaryotic cells. Sil1 may catalyse the ADP release from Bip by interacting directly with the ATPase domain of Bip. In the present study we show the complex crystal structure of the yeast Bip and the NEF Sil1 at the resolution of 2.3 Å (1 Å=0.1 nm). In the Sil1-Bip complex structure, the Sil1 molecule acts as a 'clamp' which binds lobe IIb of the Bip ATPase domain. The binding of Sil1 causes the rotation of lobe IIb ~ 13.5° away from the ADP-binding pocket. The complex formation also induces lobe Ib to swing in the opposite direction by ~ 3.7°. These conformational changes open up the nucleotide-binding pocket in the Bip ATPase domain and disrupt the hydrogen bonds between Bip and bound ADP, which may catalyse ADP release. Mutation of the Sil1 residues involved in binding the Bip ATPase domain compromise the binding affinity of Sil1 to Bip, and these Sil1 mutants also abolish the ability to stimulate the ATPase activity of Bip.