Gregory I. Goldberg, Ph.D.

DEPARTMENT OF Internal Medicine
Keywords: metalloprotease, extracellular matrix, protein structure, structure-function analysis, cell membrane

Matrix Metalloproteases (MMPs) secreted by eucaryotic cells initiate tissue remodeling by degradation of existing ECM macromolecules such as collagens and proteoglycans. These enzymes play a pivotal role in tissue remodeling during morphogenesis, wound healing, angiogenesis, uterine involution and bone resorption. Malignant cells exploit MMPs to promote tumor invasion and metastasis. The long-term goal of our laboratory is to understand the molecular mechanisms of spatial regulation of peri-cellular proteolysis catalyzed by MMPs. Our research into biological function of MMPs is based on the hypothesis that spatially regulated extracellular proteolysis is accomplished by compartmentalization of the enzymes via their interaction with molecular structures on the cell surfaces and/or macromolecules of the ECM where the physiological activation of proenzymes occurs. We combine biochemical, biophysical, molecular and cell biology approaches to study the mechanisms of extracellular proteolysis by secreted and membrane-bound metalloproteases. The mechanistic study of their interactions with the extracellular milieu and resident cells is a major focus of our attention. In this respect, the discovery of a cell surface activation mechanism of MMP-2 and isolation of its membrane activator were important breakthroughs. Our recent experiments firmly established that MMPs utilize a remarkable surface diffusion mechanism for substrate interaction. MT1-MMP, MMP-1, -2 and 9 can diffuse on the substrate surface without noticeable dissociation. Most interestingly, we have shown that activated MMP-1 is a novel type of diffusion-based ATP-independent motor enzyme that is driven by proteolysis of its substrate, collagen. Our recent results suggest that the extra-cellular portion of membrane collagenase, MT1-MMP, uses a biased diffusion mechanism for interaction with the collagen substrate, similar to that of MMP-1. Also, most instructive is the fact that the rate of diffusion of MMP-2, and -9 is not affected by complex formation with inhibitors TIMP -2 and -1, respectively. The enzyme’s C-terminal domain is required for diffusion on the substrate surface. Nevertheless, formation of a complex with inhibitor occupies a large portion of the C-terminal domain’s solvent exposed surface. Thus the inhibitor is strategically positioned on the surface of the C-terminal domain not to interfere with the diffusion process. Consequently, these findings suggest that the entire cell surface collagenolytic complex of (MT1-MMP)2/TIMP-2/MMP-2 responsible for the activation of MMP-2 is mobile relative to the underlying collagen substratum and comprises an essential part of a mobile cell surface - ECM interface. These findings have profound implications for the mechanistic understanding of the role of MMPs in spatially controlled peri-cellular collagenolysis, cell spreading, motility and invasiveness.