Extracellular protease inhibitors

Heparin has been found to bind a large number of proteins (Table 3). The biological activity of heparin and related polysaccharides is usually ascribed to their interaction with heparin-binding proteins. These proteins can be classified into classes including (1) enzymes, (2) protease inhibitors, (3) lipoproteins, (4) growth factors, (5) chemokines, (6) selectins, (7) extracellular matrix proteins, (8) receptor proteins, (9) viral coat proteins, (10) nuclear proteins, and (11) other proteins (1). Many heparin-binding proteins are enzymes and enzyme inhibitors. For example, proteases in the coagulation cascade, such as factors Ha, IXa, Xa, Xlla, and Villa, are heparin-... 

A second example of protease inhibitor design that properly illustrates the peptide scaffold-based approach is that of thrombin inhibitors. Work with these compounds led to the identification of highly potent, selective, and in vivo-effective lead compounds. A member of the serine protease family, thrombin cleaves a number of substrates (e.g., fibrinogen) and activates its platelet receptor (a G-protein-coupled receptor) by proteolysis of the extracellular N-terminal domain which results in self-activation (for a review see Reference 66). Initial lead inhibitors of thrombin were substrate-based, including the fibrinogen P3-Pi Phe-Pro-Arg sequence [67] and simple Arg derivatives such as Tos-Arg-OMe [68]. 

Several extracellular proteases have been purified and characterized from entomopathogenic fungi. Molecular weights, isoelectric points and specific inhibitors of some of these enzymes are summarized in Table 1. The majority of them belong to the family of serine proteases. 

Mammalian cell culture is the most important source of therapeutic proteins and monoclonal antibodies. Just as mammalian cells are more complicated than most other microorganisms, the media required for their growth is also more complex. The extracellular medium must provide the same nutrients and growth factors that mammalian cells are exposed to in vivo in order for them to survive, proliferate, and differentiate. Serum contains many important components that support the growth of mammalian cells including growth factors, hormones, transport and binding proteins, attachment factors, protease inhibitors, and... 

Cystatin refers to a diverse family of protein cysteine protease inhibitors. There are three general types of cystatins Type 1 (stefens), which are primarily found in the cytoplasm but can appear in extracellular fluids Type 2, which are secreted and found in most extracellular fluids and Type 3, which are multidomain protease inhibitors containing carbohydrates and that include the kininogens. Cystatin 3 is used to measure renal function in clinical chemistry. See Barrett, A.J., The cystatins a diverse superfamily of cysteine peptidase inhibitors, Biomed. Biochim. Acta 45,1363-1374,1986 Katunuma, N., Mechanisms and regulation of lysosomal proteolysis, Revis. Biol. Cellular 20, 35-61, 1989 Gauthier, F., Lalmanach, G., Moeau, T. et al., Cystatin mimicry by synthetic peptides, Biol Chem. Hoppe Seyler 373, 465-470, 1992 Bobek, L.A. and Levine,... 

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