Ge Yan, Draycheva Albena, Bornemann Thomas, Rodnina Marina V, Wintermeyer Wolfgang
Department of Physical Biochemistry, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
Nat Commun. 2014 Oct 15;5:5263. doi: 10.1038/ncomms6263.
Proteins are co-translationally inserted into the bacterial plasma membrane via the SecYEG translocon by lateral release of hydrophobic transmembrane segments into the phospholipid bilayer. The trigger for lateral opening of the translocon is not known. Here we monitor lateral opening by photo-induced electron transfer (PET) between two fluorophores attached to the two SecY helices at the rim of the gate. In the resting translocon, the fluorescence is quenched, consistent with a closed conformation. Ribosome binding to the translocon diminishes PET quenching, indicating opening of the gate. The effect is larger with ribosomes exposing hydrophobic transmembrane segments and vanishes at low temperature. We propose a temperature-dependent dynamic equilibrium between closed and open conformations of the translocon that is shifted towards partially and fully open by ribosome binding and insertion of a hydrophobic peptide, respectively. The combined effects of ribosome and peptide binding allow for co-translational membrane insertion of successive transmembrane segments.
蛋白质通过疏水跨膜片段侧向释放到磷脂双分子层中，经SecYEG转运体共翻译插入细菌质膜。转运体侧向打开的触发因素尚不清楚。在这里，我们通过光诱导电子转移（PET）监测两个附着在门边缘的SecY螺旋上的荧光团之间的侧向打开情况。在静止的转运体中，荧光被淬灭，这与封闭构象一致。核糖体与转运体结合会减少PET淬灭，表明门打开。当核糖体暴露疏水跨膜片段时，这种效应更大，并且在低温下消失。我们提出转运体的封闭和开放构象之间存在温度依赖性动态平衡，核糖体结合和疏水肽插入分别使这种平衡向部分开放和完全开放状态转变。核糖体和肽结合的综合作用使得连续的跨膜片段能够共翻译插入膜中。
