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Actin-filament motion in the in vitro motility assay has a periodic component
E L deBeer1, A M Sontrop, M S Kellermayer
1Center for Bioengineering, University of Washington, Seattle, USA.
Abstract:
The interaction between actin and myosin can be studied in the in vitro motility assay, where fluorescently labelled actin filaments are observed to move over a lawn of myosin heads. To examine details of this movement, we measured systematically the velocities of the front end, rear end, and centroid of the actin filament as the filament translated over the assay surface. We found that these velocities exhibited an unexpectedly periodic component, alternating regularly between high and low values, superimposed on the steady velocity component. The period of the oscillatory component was approximately 380 ms. When translation was stopped by an increase in osmolarity, the filaments wiggled with a periodicity similar to the translating filament, implying that wiggling and translation may be related. Rigor filaments showed no periodicity. From the frequency content of the auto- and cross-correlation functions derived from the velocities of the front end, rear end, and centroid of the actin filament, we infer a deterministic, possibly wave-like process travelling along the actin filament. Potential molecular mechanisms underlying this phenomenon are considered.
Insights
Actin filament movement over myosin shows unexpected periodic oscillations. This wiggling suggests a wave-like process, potentially linked to actin-myosin interactions.
Area of Science:
- Biophysics
- Cell Biology
- Molecular Motors
Background:
- The actin-myosin interaction is fundamental to muscle contraction and cell motility.
- The in vitro motility assay allows detailed observation of actin filament dynamics over myosin heads.
Purpose of the Study:
- To investigate the detailed movement patterns of actin filaments during in vitro motility.
- To identify and characterize any periodic components in actin filament translation.
Main Methods:
- Systematic measurement of velocities at the front end, rear end, and centroid of fluorescently labeled actin filaments.
- Analysis of velocity data using auto- and cross-correlation functions to determine frequency content.
- Observation of filament behavior under altered conditions, such as increased osmolarity and rigor states.
Main Results:
- Actin filament velocities exhibited a superimposed, periodic oscillation with a period of approximately 380 ms.
- Filament "wiggling" with similar periodicity was observed when translation was halted, suggesting a link between wiggling and translation.
- Rigor-bound filaments did not display periodicity, indicating ATP-dependent or dynamic processes are involved.
Conclusions:
- The observed periodicity suggests a deterministic, possibly wave-like process propagating along the actin filament during movement.
- This finding offers new insights into the molecular mechanisms governing actin-myosin interactions and filament dynamics.
- Further research is needed to elucidate the specific molecular basis of this oscillatory behavior.