A mechanical unfolding intermediate in an actin-crosslinking protein

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Filamin proteins crosslink F-actin filaments, crucial for cell structure.
• Their rod domains, composed of immunoglobulin (Ig) domains, vary in length and structure.
• The mechanical properties of these Ig domains are key to filamin function.

Purpose of the Study:

• Investigate the mechanics of immunoglobulin (Ig) rod domains in Dictyostelium discoideum filamin (ddFLN).
• Characterize the unfolding pathway and mechanical stability of individual Ig domains.
• Determine the role of specific amino acid sequences in domain mechanics.

Main Methods:

• Single-molecule force spectroscopy was employed to probe ddFLN Ig domains.
• Mechanical unfolding forces and contour length changes were measured.
• Analysis of unfolding patterns identified stable intermediates and mapped structural elements.

Main Results:

• One of the six Ig domains in ddFLN unfolds at significantly lower forces.
• This domain exhibits a stable unfolding intermediate.
• Amino acid inserts altered unfolding patterns, revealing a ~60 amino acid stable core.

Conclusions:

• The identified Ig domain acts as a mechanically extensible element in ddFLN.
• Fast refolding and low unfolding forces suggest a dynamic role in vivo.
• Mechanics of Ig domains are critical for the structural integrity and function of F-actin crosslinking proteins.