A Proteolytic Motor: Biased Diffusion of Collagenase and the Mechanism of Collagen Fibril Degradation
Tuesday, October 23, 2012 – 3:15pm – 4:15pm
Keir C. Neuman
Laboratory of Molecular Biophysics, NHLBI, NIH
Collagen is the main component of the extracellular matrix and plays important roles in maintaining tissue integrity. Fibrillar collagen is highly resistant to proteolysis and is primarily degraded by specific matrix metalloproteases (MMPs). Collagen degradation underlies normal physiological and pathological processes, including tissue remodeling, wound healing, and cancer metastasis. However, the process of fibrillar collagen degradation remains poorly understood. We have directly observed the process of collagen degradation by tracking individual MMP1s engaged with native type I collagen fibrils in vitro. MMP1 undergoes one-dimensional biased and hindered diffusion that is frequently interrupted by two classes of pauses. Short exponentially distributed ~0.4 s pauses occur randomly along the fiber whereas long, kinetically complex, ~1 s pauses occur predominantly at intervals of 1.3 and 1.5 µm along the fiber. 5-10 % of these long pauses are followed by the initiation of collagen proteolysis resulting in a cascade of ~15 rapid consecutive cleavages along the collagen fiber. This unidirectional motion is a ‘‘burnt bridge’’ Brownian Ratchet in which biased diffusion results from the inability of the enzyme to cross proteolyzed protein. Thus, the biased motion depends on active proteolysis of the substrate. We present a model that rationalizes these observations and provides a mechanistic paradigm for fibrillar collagen degradation.
Host: Jeff Urbach