The Structural Coupling between ATPase Activation and Recovery Stroke in the Myosin II Motor  Sampath Koppole, Jeremy C. Smith, Stefan Fischer  Structure  Volume 15, Issue 7, Pages 825-837 (July 2007) DOI: 10.1016/j.str.2007.06.008 Copyright © 2007 Elsevier Ltd Terms and Conditions

Figure 1 Lymn-Taylor Cycle The lever arm, which is attached to the myosin head via the converter domain (gray circle), swings back (during the recovery stroke, state II → III) (Malnasi-Csizmadia et al., 2001) and forth (during the power stroke, state IV → I) by 65°. Structure 2007 15, 825-837DOI: (10.1016/j.str.2007.06.008) Copyright © 2007 Elsevier Ltd Terms and Conditions

Figure 2 The Two Phases of the Coupling Mechanism (A) Prerecovery state (arrows show the motions of phase I). (B) Structure half-way along the transition pathway (arrows show the motions of phase II). (C) Postrecovery state. Straight arrows show (A) the partial closing of Switch-2 and the see-saw of the relay helix, and (B) the translation of the wedge loop and the see-saw/piston motion of the SH1 helix. The tilt of the relay helix relative to its initial orientation is indicated by the dotted line (B, left). The detailed view (middle panels) shows the two hydrogen bonds (dotted lines) formed during the two-step closing of the Switch-2 loop (A → B → C) and the wedging of the Tyr573 loop (in red) against the SH1 helix (B → C). Molecular movies of the transition pathway showing motions in this figure are at http://www.iwr.uni-heidelberg.de/groups/biocomp/fischer. Structure 2007 15, 825-837DOI: (10.1016/j.str.2007.06.008) Copyright © 2007 Elsevier Ltd Terms and Conditions

Figure 3 Structural Elements Involved in the Recovery Stroke Same coloring as in Figure 2. (A) Open and (B) closed conformations of the Switch-2 loop (green) in the end-states of the recovery stroke (same structure as in Figures 2A and 2C, respectively). The two hydrogen bonds, formed either directly (by Gly457) or indirectly (by Phe458, via Ser181 of the P loop), between Switch-2 and the γ-phosphate of ATP, are shown as dotted lines. (C) Double see-saw control of the converter domain rotation (prerecovery state in color, postrecovery state in gray): the axes of the relay helix and of the SH1 helix pivot successively by 7° and 19°, causing, respectively, 25° (rotational axis shown as a blue arrow) and 40° (axis shown as green arrow) rotations of the converter domain. The axis for the resultant overall 65° rotation is shown as red arrow (rotation axes were determined with the program DynDom [Hayward and Berendsen, 1998]). (D) Hydrophobic cradle around Phe458 side chain formed by the side chains of the wedge loop (residues 572–574). (E) The connection between converter domain (green) and myosin head (gray) consists of the SH1 helix (purple) and the relay helix (cyan and brown; the junction between the two colors indicates the location of helix unwinding). (F) Salt bridges between the converter domain and the C-terminal-third of the relay helix. Phe487 (prerecovery orientation in brown, postrecovery orientation in gray) threads (arrow) between the relay helix and the relay loop. Structure 2007 15, 825-837DOI: (10.1016/j.str.2007.06.008) Copyright © 2007 Elsevier Ltd Terms and Conditions

Figure 4 Internal Rearrangements along the Pathway (A) Rotational angle of the converter domain (thin line) and of the lever arm (thick line). (B) Change in the orientation angle (relative to prerecovery) of the relay helix (thin line, part of the helix including residues 471–485) and of the SH1-helix (thick line). (C) Hydrogen bond distances: Gly457:Namide–ATP:OγP (thick); Phe458:Ocarbonyl–Ser181:Namide (thin). (D) RMS-displacement (relative to the prerecovery structure) for atoms of the Switch-2 (thick) and of the wedge loop (thin); λ measures the overall progress of the reaction (i.e., summed RMS-difference in all atomic coordinates between successive structures along the pathway, normalized by the total length of the path). The vertical dotted lines separate phase I and phase II of the transition. Structure 2007 15, 825-837DOI: (10.1016/j.str.2007.06.008) Copyright © 2007 Elsevier Ltd Terms and Conditions

Figure 5 Mechanism of Coupling Schematic view of the three structures of Figure 2 (same coloring). (A) Prerecovery state. (B) Transition intermediate. (C) Postrecovery state. The formation of the two hydrogen bonds by the Switch-2 loop is shown as straight arrows. See Figure 2 legend for a description of the other motion arrows. Structure 2007 15, 825-837DOI: (10.1016/j.str.2007.06.008) Copyright © 2007 Elsevier Ltd Terms and Conditions