At present, representatives of the major MMPs have been successfully expressed in E. coli. Several expression systems have been utilized with or without the propeptide, including MMP catalytic domains. N and C-terminal fusion proteins with glutathione S-transferase, ubiquitin and p-galactosidase have also been also used. In the majority of cases, the expressed protein is found in IBs, even when the expressed MMP was fused to a soluble protein; an exception was the yeast ubiquitin system, which yielded soluble protein. Most workers solubilize the IBs in urea, although guanidine and cationic detergents are also effective. Refolding has been successfully carried out using a variety of techniques, including stepwise lowering of denaturant through dialysis, refolding while bound to an insoluble matrix, and pulse dilution. However, there are relatively few reports of a detailed comparison between the recombinant and native proteins.
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