Detection of small differences in actomyosin function using actin labeled with different phalloidin conjugates

Area of Science:

• Biochemistry
• Cell Biology
• Biophysics

Background:

• Actomyosin is crucial for cellular functions like muscle contraction and motility.
• Accurate measurement of actomyosin dynamics requires reliable actin filament labeling methods.
• Fluorophore labeling can potentially alter actin filament properties and assay results.

Purpose of the Study:

• To evaluate the impact of different phalloidin-based actin filament labels on actomyosin function in vitro.
• To establish a robust method for detecting subtle functional differences between various actin types.
• To explore implications for nanobiotechnology and reduce experimental costs.

Main Methods:

• In vitro motility assays were performed using actin filaments labeled with Rhodamine phalloidin (RhPh), Alexa-488 phalloidin (APh), and biotin-XX phalloidin (BPh).
• Assays were conducted under varying ionic strengths, buffer conditions (imidazole, MOPS), and MgATP concentrations.
• Dual labeling and analysis of variance were employed to compare sliding velocities and detect functional differences.

Main Results:

• Negligible differences in actomyosin function were observed among RhPh-, APh-, and BPh-labeled actin filaments.
• Variability in sliding velocity between fluorophores within a flow cell was minimal (3% SD).
• A statistically significant 4% difference in sliding velocity was detected between cardiac and skeletal muscle actin using dual labeling.

Conclusions:

• Phalloidin-based actin labeling methods (RhPh, APh, BPh) minimally affect actomyosin function in vitro motility assays.
• The developed dual-labeling method enables sensitive detection of minor functional differences in actin.
• This approach has potential applications in nanobiotechnology, fundamental actomyosin research, and reducing experimental resource use.