Phallotoxin and actin binding assay by fluorescence enhancement

Area of Science:

• Biochemistry
• Cell Biology
• Biophysics

Background:

• Phallotoxins are widely used to study actin dynamics.
• Quantifying filamentous actin (F-actin) and characterizing toxin binding is crucial for understanding cellular processes.

Purpose of the Study:

• To investigate the fluorescence properties of phallotoxin-fluorophore conjugates upon binding to F-actin.
• To establish a method for F-actin quantitation using fluorescence enhancement.
• To develop a competitive binding assay for determining phallotoxin binding constants.

Main Methods:

• Conjugating five different fluorophores to phallotoxins.
• Measuring fluorescence enhancement of conjugates upon binding to F-actin in a polymerizing buffer.
• Performing fluorescence titrations to assess binding stoichiometry.
• Conducting competition assays with various phallotoxins.

Main Results:

• Specific fluorescence enhancement was observed for all tested phallotoxin-fluorophore conjugates binding to F-actin.
• Rhodamine phalloidin exhibited the highest fluorescence enhancement (ninefold).
• Rhodamine phalloidin fluorescence showed a linear relationship with F-actin concentration up to 2 microM, enabling quantitation.
• Competition assays demonstrated that other phallotoxins could displace rhodamine phalloidin, allowing for binding constant determination.

Conclusions:

• Fluorescent phallotoxins, particularly rhodamine phalloidin, provide a sensitive and quantitative method for studying F-actin.
• This approach facilitates the accurate measurement of F-actin concentrations and the binding affinities of other phallotoxins.