Conformational changes between the active-site and regulatory light chain of myosin as determined by luminescence resonance energy transfer: The effect of nucleotides and actin

Myosin is thought to generate movement of actin filaments via a conformational change between its light-chain domain and its catalytic domain that is driven by the binding of nucleotides and actin. To monitor this change, we have measured distances between a gizzard regulatory light chain (Cys 108) and the active site (near or at Trp 130) of skeletal myosin subfragment 1 (S1) by using luminescence resonance energy transfer and a photoaffinity ATP-lanthanide analog. The technique allows relatively long distances to be measured, and the label enables site-specific attachment at the active-site with only modest affect on myosin’s enzymology. The distance between these sites is 66.8 ± 2.3 Å when the nucleotide is ADP and is unchanged on binding to actin. The distance decreases slightly with ADP-BeF(3), (−1.6 ± 0.3 Å) and more significantly with ADP-AlF(4) (−4.6 ± 0.2 Å). During steady-state hydrolysis of ATP, the distance is temperature-dependent, becoming shorter as temperature increases and the complex with ADP⋅P(i) is favored over that with ATP. We conclude that the distance between the active site and the light chain varies as Acto-S1-ADP ≈ S1-ADP > S1-ADP-BeF(3) > S1-ADP-AlF(4) ≈ S1-ADP-P(i) and that S1-ATP > S1-ADP-P(i). The changes in distance are consistent with a substantial rotation of the light-chain binding domain of skeletal S1 between the prepowerstroke state, simulated by S1-ADP-AlF(4), and the post-powerstroke state, simulated by acto-S1-ADP.