Conformational changes of plasma fibronectin detected upon adsorption to solid substrates: a spin-label study

Area of Science:

• Biochemistry
• Biophysics
• Materials Science

Background:

• Plasma fibronectin is a crucial extracellular matrix protein involved in cell adhesion and tissue repair.
• The protein's structure and function can be influenced by its interaction with surfaces.
• Understanding fibronectin's conformational changes upon surface adsorption is key to biomaterial design.

Purpose of the Study:

• To investigate the conformational changes of plasma fibronectin upon adsorption to polystyrene beads.
• To identify the specific sites within fibronectin that are affected by surface interaction.
• To correlate these structural changes with potential alterations in the protein's biological activity.

Main Methods:

• Electron spin resonance (ESR) spin-label spectroscopy was employed to probe the local environment of free sulfhydryl groups.
• Plasma fibronectin was chemically modified with a [15N, 2H]maleimide spin-label at its two free sulfhydryl groups per subunit.
• Spectra of soluble and adsorbed fibronectin were analyzed to determine the mobility of the spin-labels.

Main Results:

• Soluble fibronectin exhibited strongly immobilized ESR spectra, indicating confined environments for both sulfhydryl groups.
• Upon adsorption to polystyrene beads, half of the immobilized component converted to a weakly immobilized component.
• This spectral shift suggests that one sulfhydryl group becomes exposed and exhibits faster motion.

Conclusions:

• Adsorption of plasma fibronectin to polystyrene beads induces a conformational change.
• A buried free sulfhydryl group, located between the DNA-binding and cell-binding regions, becomes exposed.
• This exposure may significantly impact the cell adhesive properties of fibronectin.