Albany 2015:Book of Abstracts

Albany 2015
Conversation 19
June 9-13 2015
©Adenine Press (2012)

Structure and energetics of the pumping mechanism of membrane ATPase

P-class (or E1-E2-type) ATPases constitute a superfamily of cation transport enzymes, present both in prokaryote and eukaryote, whose members mediate membrane flux of all common biologically relevant cations [1]. P-class pumps use ATP to transport ions against a gradient. The sarcoplasmic reticulum Ca2+-ATPase (SERCA) pumps 2 Ca2+ from the cytosol of muscle cells to the sarcoplasmic reticulum by exchanging H+ . In each normal cycle, the Na/K pump transports 3 Na+ out of the cell by 2 K+ into the cell at the expense of the hydrolysis of one molecule of ATP. From crystallography, we now dispose of a remarkable series of snapshots showing how these enzymes look at different states of their transport cycle [2-4]. SERCA is now by far the membrane protein where the most functionally different conformations have been described in precise structural detail. Using molecular dynamics simulation and the string method with swarms-of-trajectories [5], we seek to understand the conformational dynamics involved as the pump transits through conformational states revealed by x-ray crystallography, the nature of the coupling between the binding of ATP, phosphorylation, and the movements of charged species across the core of the protein, the stepwise voltage-sensitive steps, and the origin of the ion binding specificity associated with different conformational states. A special attention is given to the protonation state of ionizable residues during the pumping cycle [6].

This research has been supported by NIH-NIGMS grant U54-GM087519.

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Benoît Roux
Huan Rui
Avisek Das

Department of Biochemistry and Molecular Biology
University of Chicago
Chicago, IL 60637

Ph: (773) 834-3557