Myosin motor domain stereo view

Figure 1.5. The waters of Thales of the myosin II motor. Stereo views of the crystal structure of the myosin motor domain of Dictostelium discoidium in presence of ATP are shown. A Space-filling display showing water molecules on a sculptured surface of the myosin II motor. B Those water molecules throughout the entire structure that are sufficiently fixed in space to be seen by X-ray diffraction are...

Especially when seen in three dimensions, as in Figure 1.5 A, the stereo view of the myosin motor domain has the appearance of a sculpted surface. The surface contains crevices and depressions, as though formed from sandstone that had been weathered by wind and rain. Only a relatively few water molecules are seen in these surface recesses, because the majority of water molecules are too mobile to be observed by X-ray diffraction. Yet these surface crevices and depressions can be filled with water molecules that, by the consilient mechanism, contribute to the energy considerations of motor function. In this regard, it should be appreciated that only 10% to 20% of the existing water molecules are sufficiently fixed in space to be located by X-ray diffraction. ... 

Fig. 15. Stereo views of the different myosin head, SI, structures showing their variable conformations in different crystal structures. (A) The heads with their motor domains superimposed and oriented as if interacting with a vertical actin filaments in the rigor conformation, Z-band bottom and M-band top. (B) The same structures in a view down the actin filament long axis, looking from the M-band towards the Z-band. Blue is the Dominguez et al. (1998) structure of SI in chicken smooth muscle with ADP.AIF4 bound, orange is the insect flight muscle SI in the ADP.Pj state (Al-Khayat et al., 2003), yellow is scallop SI crystal structure in the ADP.VO4 state (Houdusse et al., 1999), and green is the chicken skeletal muscle with no nucleotide bound (Rayment et al., 1993a).

By the hydrophobic consilient mechanism for the myosin II motor and specifically by means of AG p, ATP binding effects both hydrophobic dissociation from the actin binding site and release of the hydrophobic association at the head of the lever arm, allowing the cross-bridge to move forward toward the next attachment site. Of course, loss of phosphate would reconstitute the hydrophobic associations, that is, would effect hydrophobic re-attachment to the actin binding site in concert with re-association of the head of the lever arm with the amino-termincil domain to result in the powerstroke. Section 8.5.4 presents crystal structure stereo views from which the above-noted perspective derives. 

---

See also in sourсe #XX -- [ ]

---