Functional dissection and molecular characterization of calcium-sensitive actin-capping and actin-depolymerizing...

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Villin superfamily proteins are calcium-regulated regulators of actin assembly.
• Villin's effects on actin dynamics are concentration-dependent on calcium (Ca2+).
• Previous studies identified Ca2+-binding sites in villin but lacked functional characterization.

Purpose of the Study:

• To functionally dissect the calcium-dependent actin-capping and depolymerizing sites in villin.
• To characterize the specific roles of identified Ca2+-sensitive sites in villin's function.

Main Methods:

• Biochemical analysis of Ca2+ binding to villin (Kd, stoichiometry, Hill's coefficient).
• Identification of putative Ca2+-induced conformational change sites using NMR and crystal structures.
• Mutational analysis and molecular dynamics simulations to confirm and model functional sites.

Main Results:

• Villin binds Ca2+ with a Kd of 80.5 μM, stoichiometry of 5.97, and Hill's coefficient of 1.2.
• Six putative Ca2+-sensitive sites were identified and confirmed by mutational analysis.
• Site 1 regulates actin capping, while sites 1 and 2, along with intra-domain sites, regulate actin depolymerization.

Conclusions:

• This study provides the first sequential mutagenesis-based biochemical and functional characterization of villin's Ca2+-sensitive sites.
• Identified sites and their roles in actin capping and depolymerization offer insights into villin's calcium-dependent regulation.
• The findings lay the groundwork for understanding similar mechanisms in other villin family proteins.