Exothermic–Endothermic Transition in the Titration of Poly(allylamine chloride) with Sodium Hexametaphoshate Associated with a Change in the Proton Release Regime

2016 ◽  
Vol 120 (20) ◽  
pp. 4732-4741 ◽  
Author(s):  
Clarisse Maechling ◽  
Vincent Ball
Keyword(s):  
Proton Release ◽  
Endothermic Transition

Constant pH Molecular Dynamics Reveals How Proton Release Drives the Conformational Transition of a Transmembrane Efflux Pump

2017 ◽  
Author(s):  
Jana Shen ◽  
Zhi Yue ◽  
Helen Zgurskaya ◽  
Wei Chen
Keyword(s):  
Molecular Dynamics ◽  
Conformational Changes ◽  
Transmembrane Domain ◽  
Conformational Transition ◽  
Conformational Dynamics ◽  
Proton Release ◽  
Intrinsic Resistance ◽  
Constant Ph ◽  
Wide Range ◽  
Constant Ph Molecular Dynamics

AcrB is the inner-membrane transporter of E. coli AcrAB-TolC tripartite efflux complex, which plays a major role in the intrinsic resistance to clinically important antibiotics. AcrB pumps a wide range of toxic substrates by utilizing the proton gradient between periplasm and cytoplasm. Crystal structures of AcrB revealed three distinct conformational states of the transport cycle, substrate access, binding and extrusion, or loose (L), tight (T) and open (O) states. However, the specific residue(s) responsible for proton binding/release and the mechanism of proton-coupled conformational cycling remain controversial. Here we use the newly developed membrane hybrid-solvent continuous constant pH molecular dynamics technique to explore the protonation states and conformational dynamics of the transmembrane domain of AcrB. Simulations show that both Asp407 and Asp408 are deprotonated in the L/T states, while only Asp408 is protonated in the O state. Remarkably, release of a proton from Asp408 in the O state results in large conformational changes, such as the lateral and vertical movement of transmembrane helices as well as the salt-bridge formation between Asp408 and Lys940 and other sidechain rearrangements among essential residues.Consistent with the crystallographic differences between the O and L protomers, simulations offer dynamic details of how proton release drives the O-to-L transition in AcrB and address the controversy regarding the proton/drug stoichiometry. This work offers a significant step towards characterizing the complete cycle of proton-coupled drug transport in AcrB and further validates the membrane hybrid-solvent CpHMD technique for studies of proton-coupled transmembrane proteins which are currently poorly understood. <p><br></p>

The Proton Release Group of Bacteriorhodopsin Controls the Rate of the Final Step of Its Photocycle at Low pH†

Biochemistry ◽  
1999 ◽  
Vol 38 (7) ◽  
pp. 2026-2039 ◽  
Author(s):  
Sergei P. Balashov ◽  
Miao Lu ◽  
Eleonora S. Imasheva ◽  
Rajni Govindjee ◽  
Thomas G. Ebrey ◽  
...  
Keyword(s):  
Low Ph ◽  
Proton Release ◽  
Release Group

scholarly journals Light-Induced Proton Release by the Cyanobacterium Anabaena variabilis

1988 ◽  
Vol 86 (3) ◽  
pp. 769-772 ◽  
Author(s):  
Siegfried Scherer ◽  
Heike Riege ◽  
Peter Böger
Keyword(s):  
Anabaena Variabilis ◽  
Proton Release ◽  
Cyanobacterium Anabaena

scholarly journals Structural Changes Due to the Deprotonation of the Proton Release Group in the M-Photointermediate of Bacteriorhodopsin as Revealed by Time-Resolved FTIR Spectroscopy†

Biochemistry ◽  
2008 ◽  
Vol 47 (44) ◽  
pp. 11598-11605 ◽  
Author(s):  
Joel E. Morgan ◽  
Ahmet S. Vakkasoglu ◽  
Johan Lugtenburg ◽  
Robert B. Gennis ◽  
Akio Maeda
Keyword(s):  
Ftir Spectroscopy ◽  
Structural Changes ◽  
Proton Release ◽  
Time Resolved ◽  
Release Group
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