Sequence-dependent mechanics of collagen reflect its structural and functional organization

Area of Science:

• Biophysics
• Materials Science
• Cell Biology

Background:

• Extracellular matrix (ECM) mechanics are crucial for cellular functions.
• The mechanical properties of collagen proteins, particularly network-forming collagen IV in basement membranes, are poorly understood.
• Collagen IV features interruptions in its triple-helix sequence, distinguishing it from fibril-forming collagens.

Purpose of the Study:

• To investigate the impact of sequence heterogeneity on the local flexibility of collagen IV and collagen III.
• To determine how interruptions in the collagen IV sequence influence its mechanical properties.
• To compare the flexibility profiles of network-forming and fibril-forming collagens.

Main Methods:

• Atomic force microscopy (AFM) was employed to measure the local flexibility of collagen IV and collagen III.
• A modeling approach was used to correlate flexibility with sequence interruptions.
• Flexibility was assessed under varying pH and chloride concentrations.

Main Results:

• Collagen IV displays highly heterogeneous mechanics, with regions of high flexibility, particularly near the N-terminus, attributed to sequence interruptions.
• Sequence interruptions significantly enhance local flexibility in collagen IV, influencing chain alignment.
• Collagen III shows a flexible region near its matrix-metalloprotease binding site, suggesting a unique mechanical fingerprint for matrix remodeling.
• Proline content did not correlate with local flexibility in either collagen type.
• Changes in pH and chloride concentration did not affect collagen IV flexibility.

Conclusions:

• Sequence interruptions are the primary drivers of collagen IV's heterogeneous mechanical properties.
• The unique flexibility profile of collagen IV is critical for basement membrane structure and function.
• Environmental factors like pH and chloride concentration do not modulate collagen IV's intrinsic flexibility.
• Understanding collagen mechanics provides insights into ECM remodeling and cellular signaling.