In this lecture we present evidence for the ratchet mechanism at work for PcrA helicase, one of the smallest motor proteins structurally known and, hence, amenable to rigorous analysis. We demonstrate a mechanism in which, during one ATP hydrolysis cycle, the pulling together and pushing apart of two PcrA domains is synchronized with alternating mobilities of the individual domains such that PcrA moves unidirectionally along single stranded DNA. Multiscale modeling involving quantum mechanical, classical mechanical, and stochastic calculations shows in particular how ATP binding and subsequent hydrolysis influence in a highly delocalized fashion the ability of the individual PcrA domains to move along DNA. The mechanism seen is supported by a variety of computational analysis methods, that offer thereby an atomic level view of PcrA's ratchet type motion along DNA. Our investigation revealed also a close similarity between structures and reaction pathways in PcrA helicase and in F1-ATPase, the latter being a motor found in every biological cell. This suggests that the mechanochemical mechanism identified in PcrA helicase is actually shared by many other biological motors.
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 Markus Dittrich and Klaus Schulten. PcrA helicase, a prototype ATP-driven molecular motor. Structure, 14:1345-1353, 2006.
 Jin Yu, Taekjip Ha, and Klaus Schulten. Structure-based model of the stepping motor of PcrA helicase. Biophysical Journal, 91:2097-2114, 2006
 Markus Dittrich, Jin Yu, and Klaus Schulten. PcrA helicase, a molecular motor studied from the electronic to the functional level. Topics in Current Chemistry, 268:319-347, 2006.
 Jin Yu, Taekjip H, and Klaus Schulten. How Directional Translocation is Regulated in a DNA helicase motor. Biophysical Journal, 93:3783-3797, 2007.