scholarly journals Author response: Two-way communication between SecY and SecA suggests a Brownian ratchet mechanism for protein translocation

Author(s):  
William John Allen ◽  
Robin Adam Corey ◽  
Peter Oatley ◽  
Richard Barry Sessions ◽  
Steve A Baldwin ◽  
...  
eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
William John Allen ◽  
Robin Adam Corey ◽  
Peter Oatley ◽  
Richard Barry Sessions ◽  
Steve A Baldwin ◽  
...  

The essential process of protein secretion is achieved by the ubiquitous Sec machinery. In prokaryotes, the drive for translocation comes from ATP hydrolysis by the cytosolic motor-protein SecA, in concert with the proton motive force (PMF). However, the mechanism through which ATP hydrolysis by SecA is coupled to directional movement through SecYEG is unclear. Here, we combine all-atom molecular dynamics (MD) simulations with single molecule FRET and biochemical assays. We show that ATP binding by SecA causes opening of the SecY-channel at long range, while substrates at the SecY-channel entrance feed back to regulate nucleotide exchange by SecA. This two-way communication suggests a new, unifying 'Brownian ratchet' mechanism, whereby ATP binding and hydrolysis bias the direction of polypeptide diffusion. The model represents a solution to the problem of transporting inherently variable substrates such as polypeptides, and may underlie mechanisms of other motors that translocate proteins and nucleic acids.


2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Joshua W. McCausland ◽  
Xinxing Yang ◽  
Georgia R. Squyres ◽  
Zhixin Lyu ◽  
Kevin E. Bruce ◽  
...  

AbstractThe FtsZ protein is a central component of the bacterial cell division machinery. It polymerizes at mid-cell and recruits more than 30 proteins to assemble into a macromolecular complex to direct cell wall constriction. FtsZ polymers exhibit treadmilling dynamics, driving the processive movement of enzymes that synthesize septal peptidoglycan (sPG). Here, we combine theoretical modelling with single-molecule imaging of live bacterial cells to show that FtsZ’s treadmilling drives the directional movement of sPG enzymes via a Brownian ratchet mechanism. The processivity of the directional movement depends on the binding potential between FtsZ and the sPG enzyme, and on a balance between the enzyme’s diffusion and FtsZ’s treadmilling speed. We propose that this interplay may provide a mechanism to control the spatiotemporal distribution of active sPG enzymes, explaining the distinct roles of FtsZ treadmilling in modulating cell wall constriction rate observed in different bacteria.


2010 ◽  
Vol 120 (6) ◽  
pp. 901-925 ◽  
Author(s):  
Andrej Depperschmidt ◽  
Peter Pfaffelhuber

2020 ◽  
Author(s):  
Hisham Mazal ◽  
Marija Iljina ◽  
Inbal Riven ◽  
Gilad Haran

AbstractAAA+ ring-shaped machines, such as ClpB and Hsp104, mediate substrate translocation through their central channel by a set of pore loops. Recent structural studies suggested a universal hand-over-hand translocation mechanism, in which pore loops are moving rigidly in tandem with their corresponding subunits. However, functional and biophysical studies are in discord with this model. Here, we directly measure the real-time dynamics of the pore loops of ClpB and their response to substrate binding, using single-molecule FRET spectroscopy. All pore loops undergo large-amplitude fluctuations on the microsecond timescale, and change their conformation upon interaction with substrate proteins. Pore-loop conformational dynamics are modulated by nucleotides and strongly correlate with disaggregation activity. The differential behavior of the pore loops along the axial channel points to a fast Brownian-ratchet translocation mechanism, which likely acts in parallel to the much slower hand-over-hand process.


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