Intermolecular Misfolding Captured in Parallelly Organized Titin.

Area of Science:

• Muscle physiology
• Biophysics
• Protein folding

Background:

• Titin, a giant muscle protein, provides passive muscle elasticity through its immunoglobulin (Ig) domains.
• These Ig domains unfold and refold under mechanical stress during muscle stretching.
• Existing research on titin elasticity primarily uses single-molecule experiments, overlooking its native parallel organization.

Purpose of the Study:

• To investigate the impact of titin's parallel organization on immunoglobulin (Ig) domain folding and muscle elasticity.
• To directly observe intermolecular misfolding in parallel-arranged titin Ig domains.

Main Methods:

• Employed two-molecule force spectroscopy to study titin's behavior in a parallel arrangement.
• Focused on the I-band region of titin, specifically the I94 domains.

Main Results:

• Directly observed intermolecular misfolding of titin immunoglobulin (Ig) domains in a parallel setup.
• Demonstrated that two parallel I94 domains can form a stable, intermolecular domain-swapped state.
• This misfolded state exhibits thermal and mechanical stability.

Conclusions:

• Parallel organization of titin influences immunoglobulin (Ig) domain folding, leading to intermolecular misfolding.
• Intermolecularly misfolded titin domains form stable structures.
• This phenomenon may have significant roles in titin organization and muscle elasticity.