Potential proteolytic activity of human plasma fibronectin

Area of Science:

• Biochemistry
• Molecular Biology
• Proteomics

Background:

• Fibronectin (FN) is a crucial extracellular matrix glycoprotein involved in cell adhesion and migration.
• The presence of latent enzymatic activity within FN has not been previously established.

Purpose of the Study:

• To investigate the potential for latent proteinase activity within human plasma fibronectin.
• To characterize the enzymatic activity and its relationship to FN fragments.

Main Methods:

• Human plasma FN was digested with cathepsin D and separated into fragments using heparin-Sepharose chromatography.
• Proteolytic activity was assessed using NaDodSO4/polyacrylamide gel electrophoresis with gelatin or fibrinogen copolymerized gels.
• Inhibition assays were performed using SH proteinase inhibitors and 125I-labeled cystatin.

Main Results:

• A 140-kDa single-chain fragment (H-1) of FN exhibited spontaneous proteolytic degradation.
• Subfragments of H-1 yielded a proteolytically active doublet of 28-30 kDa.
• The activity was sensitive to SH proteinase inhibitors and formed a complex with cystatin, indicating it is an SH proteinase.

Conclusions:

• Human plasma fibronectin contains a latent SH proteinase activity within its central domain.
• This proteinase can be released and activated, potentially playing a role in matrix remodeling.
• Structural similarities suggest a possible dual role for the FN fragment as both a proteinase and an inhibitor.