Abstract
Based on recent structural and functional findings, we have constructed
a mathematical model for the sodium-driven Fo motor of the F1Fo-ATPase
from the anaerobic bacterium Propionigenium modestum. The model reveals
the mechanochemical principles underlying the Fo motor's operation,
and explains all of the existing experimental data on wild-type and
mutant Fo motors. In particular, the model predicts a nonmonotonic
dependence of the ATP hydrolysis activity on the sodium concentration,
a prediction confirmed by new experiments. To explain experimental
observations, the positively charged stator residue (R227) must assume
different positions in the ATP synthesis and hydrolysis directions.
This work also illustrates how to extract a motor mechanism from
dynamical experimental observations in the absence of complete structural
information.
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