A six-armed oligomer isolated from cell surface fibronectin preparations

Area of Science:

• Biochemistry
• Cell Biology
• Structural Biology

Background:

• Fibronectins are key adhesive glycoproteins mediating cell-substrate attachment.
• Plasma fibronectin (PFN) is a dimer (220,000 MW subunits) with a long, flexible strand structure.
• Cells produce extracellular matrix fibronectin and cell surface fibronectin (CSFN).

Purpose of the Study:

• To investigate the structure of cell surface fibronectin (CSFN) molecules.
• To compare the structure of CSFN dimers and oligomers with plasma fibronectin (PFN).

Main Methods:

• Electron microscopy was used to examine CSFN structure.
• Zone sedimentation through glycerol gradients separated CSFN dimers, oligomers, and contaminants.
• Structural comparison was made between PFN and CSFN forms.

Main Results:

• CSFN dimers were found to be structurally identical to PFN.
• CSFN oligomers exhibited a novel 'hexabrachion' structure with six arms from a central particle.
• The arms of the hexabrachion, while similar to PFN, possessed distinct features.

Conclusions:

• Cell surface fibronectin (CSFN) exists in at least two distinct structural forms: dimers identical to plasma fibronectin (PFN) and a unique hexabrachion oligomer.
• The hexabrachion represents a complex, well-defined structure not previously described for fibronectin.
• Further investigation into the distinct structural and functional properties of hexabrachions is warranted.