Single molecule images for: An empirical energy landscape reveals mechanism of proteasome in polypeptide translocation

The ring-like ATPase complexes in the AAA+ family perform diverse cellular
functions that require coordination between the conformational transitions
of their individual ATPase subunits.  How the energy from ATP
hydrolysis is captured to perform mechanical work by these coordinated
movements is not known.  In this study, we developed a novel
approach for delineating the nucleotide-dependent free-energy landscape
(FEL) of the proteasome's heterohexameric ATPase complex based on
complementary structural and kinetic measurements.  We used the
FEL to simulate the dynamics of the proteasome and quantitatively
evaluated the predicted structural and kinetic properties. The FEL model
predictions were widely consistent with experimental observations in this
and previous studies and suggested novel features of the mechanism of
proteasomal ATPase. We find that the cooperative movements of the ATPase
subunits result from the design of the ATPase hexamer entailing a unique
free-energy minimum for each nucleotide-binding state.  ATP
hydrolysis dictates the direction of substrate translocation by triggering
an energy-dissipating conformational transition of the ATPase complex.