Intermolecular interaction of actin revealed by a dynamic light scattering technique

Area of Science:

• Biophysics
• Biochemistry

Background:

• Actin is a crucial protein for cell structure and motility.
• Understanding actin's intermolecular forces is essential for elucidating its biological functions.

Purpose of the Study:

• To investigate the intermolecular interaction forces of monomeric actin.
• To determine the applicability of Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to actin interactions.

Main Methods:

• Dynamic light scattering (DLS) was employed to measure mutual diffusion coefficients.
• Analysis involved varying potassium chloride (KCl) concentrations in a G-buffer.

Main Results:

• The translational diffusion coefficient of monomeric actin was determined as D(0) = (87 +/- 3) x 10(-12) m(2).s(-1).
• This yielded a hydrodynamic radius (r(H)) of 2.8 +/- 0.1 nm.
• Extended DLVO theory, incorporating an additional repulsive potential, successfully described actin-actin interactions, unlike the standard DLVO theory.
• The Hamaker constant for Ca(2+)-ATP bound actin was determined to be A(H) = 10.4 +/- 0.6 k(B)T.

Conclusions:

• Standard DLVO theory is insufficient to model actin's intermolecular forces.
• Extended DLVO theory provides a better framework for understanding actin interactions.
• This study provides the first determination of the Hamaker constant for Ca(2+)-ATP bound actin.