Collagen pretzels revealed by electron microscopy

Area of Science:

• Biochemistry
• Structural Biology
• Cell Biology

Background:

• Collagen XV is a large, multidomain structural protein crucial for skeletal muscle and capillaries.
• Its complex structure and proteoglycan nature hinder high-resolution structural analysis.
• Previous studies lacked detailed structural data due to collagen's inherent properties.

Discussion:

• Rotary shadowing electron microscopy revealed detailed images of purified collagen XV molecules.
• The N-terminus exhibits a distinct three-lobed structure, and individual glycosaminoglycan chains are visible.
• Collagen XV molecules form unique, knotted, pretzel-like structures, challenging conventional views of collagen morphology.

Key Insights:

• Collagen XV molecules multimerize into cruciform structures, with simpler complexes containing two to four molecules.
• Immunoelectron microscopy demonstrated these complexes bridging collagen fibrils near basement membranes.
• The study successfully purified collagen XV from human umbilical cord, despite its low abundance.

Outlook:

• These findings offer unprecedented structural insights into collagen XV.
• Understanding collagen XV's structure may elucidate its role in tissue integrity and disease.
• Further research can explore the functional implications of its unique quaternary structure.