Cells Control BIN1-Mediated Membrane Tubulation by Altering the Membrane Charge

Area of Science:

• Cell Biology
• Biochemistry
• Structural Biology

Background:

• Bridging integrator 1 (BIN1) is a muscle-specific protein belonging to the BAR protein family, crucial for membrane bending.
• BIN1 plays a significant role in muscle development and is implicated in skeletal myopathies.

Purpose of the Study:

• To investigate BIN1's ability to form tubular membrane structures in vitro.
• To elucidate the role of electrostatic interactions in BIN1-mediated membrane bending and binding.
• To understand how membrane charge and curvature influence BIN1 function and its implications in myopathies.

Main Methods:

• In vitro tubulation assays using BIN1 protein.
• Liposome-based experiments to study the effect of lipid composition and membrane curvature on BIN1 binding.
• Cell-based assays with manipulated membrane charge and BIN1 mutants.
• Analysis of BIN1's surface charge properties and electrostatic interactions.

Main Results:

• BIN1 alone can form complex interconnected tubular systems in vitro, mimicking muscle t-tubules.
• BIN1's membrane bending and binding are regulated by electrostatic interactions, influenced by lipid charge ratio and BIN1's surface charge.
• Membrane charge and curvature significantly affect BIN1's binding and bending capabilities, with reduced function observed at lower membrane charges and high curvatures.
• BIN1 mutants lacking key charges in the BAR domain exhibit reduced membrane bending, a phenotype rescued by increasing negative membrane charge.

Conclusions:

• BIN1's electrostatic interactions are critical for its membrane bending and tubulation activities.
• Cellular membrane charge is a key regulator of BIN1 function and recruitment of associated proteins like dynamin.
• Understanding BIN1-membrane charge interactions provides insights into the molecular mechanisms of myopathies and potential therapeutic strategies.