Protein Gels Degradation by Proteases

Tissues and organs are formed by specialized cells and by extracellular matrix (ECM) organized in 3-dimensional (3D) structure. ECM is a mix of various components, mainly of proteins. ECM remodeling is a physiological and pathological phenomenon (Raeber et al 2005). During tumor dissemination, invasive cells must liquefy the matrix to invade other tissues and establish distant metastases. Many groups study cancer cell behavior; however, up to now, few experimental data are focused on understanding the physical aspect of ECM degradation by enzymes.The aim of this work is to find general behavior able to describe the physical mechanism of ECM enzymatic degradation.Previous experimental studies have shown that the gelatin-gel degradation kinetics by thermolysin, a metalloproteinase, is diffusion limited (Lairez et al, 2007). A power law dependence on degradation time as a function of enzyme concentration was found and associated to a self-attracting enzyme random walk, leading to a continuum percolation model for proteolysis. Recently, we have demonstrated the same behavior with 2 serine proteases, trypsin and proteinase K (Breton et al, in preparation).Here we study protein gel degradation by papain (a cystein protease) and chymotrypsin (a serine protease) by varying solvent viscosity, gelatin and enzyme concentrations. We obtain either a linear dependency or a power law of the degradation time (tc) as a function of enzyme concentrations: tc α 1/[papain]1.1+/-0.1 and tc α 1/[chymotrypsin]1.9+/-0.15. In the presence of glycerol, gel degradation kinetics with papain is reaction limited and enzyme diffusion is Brownian. With chymotrypsin, tc increase and can be superimposed to those obtained without glycerol by taking into account both, the enzyme activity decrease and the solvent viscosity increase. Gel proteolysis kinetics is therefore diffusion limited and the diffusion is anomalous. We discuss possible explanation for these different mechanisms.