Connectin: cell surface protein that binds both laminin and actin

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Cell surface receptors play crucial roles in mediating cell interactions with the extracellular matrix.
• Laminin is a key component of the extracellular matrix involved in cell adhesion and migration.
• Actin is a critical intracellular protein involved in cell structure and motility.

Purpose of the Study:

• To identify and characterize a novel cell surface receptor protein from mouse fibrosarcoma cells.
• To investigate the binding properties of this receptor with actin and laminin.
• To elucidate the potential function of this receptor in cell-matrix interactions.

Main Methods:

• Purification of a 70,000 Mr cell surface receptor protein from mouse fibrosarcoma cells.
• Cosedimentation assays and filter binding assays to demonstrate receptor-actin binding.
• Scatchard analysis to determine the binding affinity (Kd) of the receptor for actin.
• Viscosity measurements and filament bundling observations to assess the effect of the receptor on actin filaments.

Main Results:

• A 70,000 Mr protein, named connectin, was purified and shown to bind actin with high affinity (Kd = 6 X 10(-7) M).
• Connectin demonstrated specificity for actin binding, as shown by displacement assays.
• Connectin reduced actin filament viscosity and induced parallel filament bundling, suggesting binding along filament sides.
• Connectin's ability to bind both extracellular laminin and intracellular actin was established.

Conclusions:

• Connectin is a novel cell surface receptor with dual binding capabilities for extracellular laminin and intracellular actin.
• Connectin may function as a transmembrane protein, bridging the cell's interior with the extracellular matrix.
• This interaction mediated by connectin could be critical for regulating cell adhesion, migration, and overall cell-matrix communication.