Direct visualization of extensibility in isolated titin molecules

Area of Science:

• Biophysics
• Molecular Biology
• Protein Mechanics

Background:

• Titin molecules are crucial for muscle elasticity.
• Understanding titin's mechanical properties is key to muscle function.

Purpose of the Study:

• To investigate the mechanical extension of individual titin molecules.
• To identify regions of titin responsible for extensibility.

Main Methods:

• Utilizing "molecular combing" technique induced by a receding meniscus.
• Employing electron microscopy to visualize titin molecule extension.
• Analyzing forces applied to titin molecules up to approximately 800 pN.

Main Results:

• Titin molecules were observed to extend significantly, with forces up to 800 pN.
• Both ends of the titin molecule tend to adhere to a mica substrate.
• A specific I-band region, rich in P, E, V, and K residues, showed the highest compliance, extending via polypeptide chain unfolding.
• Other regions of the titin molecule also exhibited extensibility.

Conclusions:

• Molecular combing effectively extends titin molecules, allowing for mechanical analysis.
• The compliance of titin is sequence-dependent, with a specific region undergoing unfolding.
• Mechanical extensions of titin are likely reversible, suggesting a role in muscle recoil.