Microtubule conformational change

DMP also has been used to study the interaction between the endoplasmic reticulum and microtubules (Ogawa-Goto et al., 2007), the conformational changes in the outer arm dynein of Chlamydomonas in response to calcium (Sakato et al., 2007), and the secretion of the adipocyte-specific secretory protein adiponectin (Wang et al., 2007). 

Fast transport in cells requires vehicles (the organelles or vesicles), motors and fuel. The motors can be divided into two families, the cytoplasmic dyneins and the kinesins (Fig. 5-35). Each uses ATP as a fuel, the energy being provided by its hydrolysis to ADP and P . The motors can sense the polarity of the microtubules dyneins drive toward the minus end, while most kinesins drive toward the plus end. Movement is generated by cyclic hydrolysis of ATP, conformational changes, and the reversible attachment to microtubules. 

These are Ca -binding proteins found in the brain and the central nervous system, which belong to the same branch of the calmodulin family as the intestinal proteins, to which they are closely related. Both contain one variant and one normal " site for Ca . The SlOO protein exists in two forms, a and b. Binding of calcium results in conformational change. The SlOOb protein also binds two Zn ions, with conformational change, and with higher affinity than Ca. Zn is involved with the tubulin microtubule system in brain. SlOOb may be associated with this process. 

Figure 34.24 Krnesin moving along a microtubule. (1) One head of a two-headed kinesin molecule, initially with both heads in the ADP form, binds to a microtubule. (2) The release of ADP and the binding of ATP results in a conformational change that locks the head to the microtubule and pulls the neck linker (orange) to the head domain, throwing the second domain toward the plus end of the microtubule. (3) ATP undergoes hydrolysis while the second head interacts with the microtubule.

FIGURE 3-23 Motor protein-dependent movement of cargo. The head domains of myosin, dynein, and kinesin motor proteins bind to a cytoskeletal fiber (microfilaments or microtubules), and the tail domain attaches to one of various types of cargo—in this case, a membrane-limited vesicle. Hydrolysis of ATP in the head domain causes the head domain to "walk" along the track in one direction by a repeating cycle of conformational changes. 

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