Fibrous mini-collagens in hydra nematocysts

Area of Science:

• Cell Biology
• Biophysics
• Zoology

Background:

• Nematocysts (cnidocysts) are unique exocytotic organelles essential for cnidarian survival.
• Their structural integrity under high pressure is critical for function.

Purpose of the Study:

• To elucidate the structural organization of the nematocyst capsule wall.
• To identify the molecular components contributing to its mechanical properties.

Main Methods:

• Atomic force microscopy (AFM) was employed to visualize nanoscale surface topography.
• Field emission scanning electron microscopy (FESEM) provided high-resolution imaging of the capsule wall.

Main Results:

• The outer nematocyst wall comprises globular proteins of undetermined function.
• The inner wall features collagen-like fibrils with specific spacing (50-100 nm) and cross-striations (32 nm).
• These fibrils are polymers of "mini-collagens," known from Hydra nematocysts, providing tensile strength against 15 MPa osmotic pressure.

Conclusions:

• The distinct fibrillar structure of the inner nematocyst wall is crucial for withstanding high internal pressures.
• Mini-collagen polymers are key components conferring mechanical resilience to cnidarian stinging organelles.