Abstract
This review focusses on the energetics of protein translocation via the Sec translocation machinery. First we complement structural data about SecYEG’s conformational rearrangements by insight obtained from functional assays. These include measurements of SecYEG permeability that allow assessment of channel gating by ligand binding and membrane voltage. Second we will discuss the power stroke and Brownian ratcheting models of substrate translocation and the role that the two models assign to the putative driving forces: (i) ATP (SecA) and GTP (ribosome) hydrolysis, (ii) interaction with accessory proteins, (iii) membrane partitioning and folding, (iv) proton motive force (PMF), and (v) entropic contributions. Our analysis underlines how important energized membranes are for unravelling the translocation mechanism in future experiments.
Highlights
Structural Insights into SecY Conformational States During TranslocationThe Sec machinery is responsible for the reconstitution and translocation of many bacterial cytoplasmic, outer membrane and secretory proteins
The core element of the Sec translocation machinery is the heterotrimeric translocon SecYEG which resides in the cytoplasmic membrane
The main translocation unit of the translocon SecY can be seen as a clamshell with a hinge region clamped by SecE, and the so-called lateral gate—composed of transmembrane helixes TM2b and TM7 on opposite sides
Summary
Structural Insights into SecY Conformational States During TranslocationThe Sec machinery is responsible for the reconstitution and translocation of many bacterial cytoplasmic, outer membrane and secretory proteins. Structural Insights into SecY Conformational States During Translocation
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