************OWARI COMPLEX SEMINAR LIII************

Title : Phosphate release coupled to rotary motion 
of F1-ATPase

Speaker : Dr. Kei-ichi Okazaki

Affiliation : National Institutes of Health (NIH), 
USA

Date : Thu. Jul. 18th, 13:30 pm (Almost one hour)

Place : 1F 2nd lecture Room, Graduate School of 
Information Science

Abstract :
F1-ATPase, the catalytic domain of ATP synthase, 
synthesizes most of the ATP in living organisms. 
Running in reverse powered by ATP hydrolysis, this 
hexameric ring-shaped molecular motor formed by 
three αβ-dimers creates torque on its central 
γ-subunit. This reverse operation enables detail-
ed explorations of the mechanochemical coupling 
mechanisms in experiment and simulation. Here, 
we use molecular dynamics simulations to construct 
a first atomistic conformation of the intermediate 
state following the 40°-substep of rotary motion, 
and to study the timing and molecular mechanism of 
inorganic phosphate (Pi) release coupled to the 
rotation. In response to torque-driven rotation of 
the γ-subunit in the hydrolysis direction, the 
nucleotide-free αβE interface forming the "empty" 
E-site loosens and singly charged Pi readily 
escapes to the P-loop. By contrast, the interface 
stays closed with doubly charged Pi. The γ-
rotation tightens the ATP-bound αβTP interface, 
as required for hydrolysis. The calculated rate 
for the outward-release of doubly charged Pi from 
the αβE interface 120° after ATP hydrolysis 
closely matches the ~1 ms functional timescale. 
Conversely, Pi release from the ADP-bound αβDP 
interface postulated in earlier models would occur 
through a kinetically infeasible inward-directed 
passage. Our simulations help reconcile conflicting 
interpretations of single-molecule experiments and 
crystallographic studies by clarifying the timing 
of Pi exit, its pathway and kinetics, associated 
changes in Pi protonation, and changes of the F1-
ATPase structure in the 40o-substep. Important 
elements of the molecular mechanism of Pi release 
emerging from our simulations appear to be conserved 
in myosin in spite of the different functional 
motions.

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