Structural Elements Required for Phosphorylation-Dependent Activation

Structural Elements Required for Phosphorylation-Dependent Activation 

The mechanism to account for phosphorylation-dependent activation of myosin s motor properties is more complex than the interactions that stabilize the folded monomer. Mutation of S19 of the RLC to either D or E did not activate myosin s motor properties, but mutating both T18 and S19 to negatively charged amino acids partially activated motility (Sweeney et al., 1994) and ATPase activity (Kamisoyama etal., 1994). In contrast, rapid actin movement was supported by myosin whose RLC was phosphorylated at either T18 or S19, suggesting that the interaction formed upon activation has specific spatial constraints that are satisfied only by a phosphate moiety (Sweeney etal., 1994). 

RLC removal does not produce a normal on state like that obtained upon phosphorylation. RLC-deficient myosin has an approximately 6-fold lower actin-activated ATPase activity that is coupled to a 10-fold decrease in the velocity of actin movement (=0.1 xm/sec versus 1 xm/sec for native myosin, 30°C) (Trybus et al., 1994). RLC removal also increases the basal myosin MgATPase activity 10-fold (from 0.02 sec i to 

Importance of the C-Terminal Half of the Regulatory Light Chain 

When skeletal muscle RLC was incorporated into smooth muscle myosin, the hybrid molecule could no longer be activated by phosphorylation (note that skeletal RLC contains a homologous phosphorylatable ser- 

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B. Structural Elements Required for Phosphorylation-Dependent Activation... 

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