Key Points
- Investigate the molecular mechanism underlying actin filament velocity differences caused by converter domain substitutions in Drosophila chimeric myosin isoforms.
- Assessed native indirect flight muscle (IFI) and chimeric (IFI-EC) Drosophila myosins via laser trap assays to measure unitary step displacement.
- Performed basal and actin-activated ATPase assays along with skinned muscle fiber mechanical experiments to quantify enzymatic and kinetic behavior.
- Unitary step displacement remained consistent between native IFI (7.3 ± 1.0 nm) and chimeric IFI-EC myosin (5.8 ± 0.9 nm; means ± SE) in laser trap assays.
- ATPase activity and skinned fiber mechanical data confirmed that altered strong actin-myosin binding kinetics, rather than changes in mechanical step capacity, govern actin filament velocity.
Structured PICO
PPopulationDrosophila chimeric myosin isoforms (embryonic body wall muscle [EMB] and indirect flight muscle [IFI])
IInterventionGenetic substitution of the converter domains (EMB-IC and IFI-EC chimeric myosin proteins)
CComparatorWild-type myosin isoforms (IFI and EMB)
OOutcomeActin filament velocity (V(actin)) and unitary step displacementsurrogate
The converter domain of Drosophila myosin modulates the kinetic properties of strong actin-myosin binding, likely coupling the Pi and ADP release steps during the cross-bridge cycle.