ABSTRACT
Our knowledge of how motor proteins work comes from many different experimental sources. It is important to note that multiple experimental methods give us complementary information on various aspects of biological molecular motor functioning. Bulk biochemical kinetic studies provide an average dynamic description of relevant chemical processes associated with motor proteins, including equilibrium constants, relaxation times to stationary states, chemical reaction rates, and changes in concentrations of motor species with time (De La Cruz and Ostap 2004, Fischer et al. 2010, Gilbert and Mackey 2000) [38, 54, 61]. Structural studies allow researchers to determine spatial positions of various atoms in different molecular conformations, and they also help to choose the most relevant chemical states from the point of view of supporting dynamics of molecular motors (Howard 2001, Rice et al 1999, Sweeney and Houdusse 2010, Kozielski et al. 1997, Marx et al. 2005, Marx et al. 2009) [68, 132, 161, 88, 107, 106]. Single-molecule investigations concentrate on dynamic and mechanical properties of individual molecules during their motion on various cellular structures (Howard 2001, Veigel and Schmidt 2011, Green-
leaf et al. 2007, Dulin et al. 2013) [68, 175, 63, 46]. The crucial observation is that these methods allow modifications of the activities of individual motors via applying external loads and changing rates of chemical transitions. Microscopy measurements lead to visualization of motor protein molecules in different biochemical states (Veigel and Schmidt 2011, Greenleaf et al. 2007) [175, 63]. To understand the fundamental mechanisms of motor proteins, one has to combine and utilize all information obtained by different techniques. However, a critical analysis of what these experiments actually can tell us is needed. There are drawbacks, limitations, uncertainties, and specific assumptions associated with each method, and these factors should be taken into account if we wish to fully understand how motor proteins function.
