Trypsin inhibitors folding

Figure 2.14 shows examples of both cases, an isolated ribbon and a p sheet. The isolated ribbon is illustrated by the structure of bovine trypsin inhibitor (Figure 2.14a), a small, very stable polypeptide of 58 amino acids that inhibits the activity of the digestive protease trypsin. The structure has been determined to 1.0 A resolution in the laboratory of Robert Huber in Munich, Germany, and the folding pathway of this protein is discussed in Chapter 6. Hairpin motifs as parts of a p sheet are exemplified by the structure of a snake venom, erabutoxin (Figure 2.14b), which binds to and inhibits... 

Weissman, J.S., Kim, P.S. Kinetic role of non-native species in the folding of bovine pancreatic trypsin inhibitor. Proc. Natl. Acad. Sci. USA 89 9900-9904, 1992. 

Despite their lack of stabilizing disulfide bridges Potl inhibitors feature a common, stable fold. The N-terminus is coiled, although in some structures a small /3-strand has been identified. After a turn the structure adopts an a-helical structure, followed by a turn and an other /3-strand. The sequence then features an extended turn or loop motif that contains the reactive site of the inhibitor before it proceeds with a /3-strand running almost parallel to the /3-strand after the a-helix. After another turn and coiled motif a short /3-strand antiparallel to the other /3-strands precedes the coiled C-terminus. Usually the N-terminal residue in the reactive site is an acidic residue followed by an aromatic amino acid, that is, tyrosine or phenylalanine. Figure 11 shows the complex of chymotrypsin inhibitor (Cl) 2 with subtilisin, the hexamer of Cl 2 from H. vulgare and a structural comparison with a trypsin inhibitor from Linum usitatissimum ... 

Several such hydration models have been evaluated in terms of their abilities to discriminate among various folded forms of bovine pancreatic trypsin inhibitor (BPTI)97-99. In this approach, the free energy of hydration, V, is added to the conformational energy of the oligopeptide in the absence of solvent, U, of Eq. [1], to obtain the total conformational energy, G ... 

G. Wagner, W. Braun, T. F. Havel, T. Schaumann, N. Go, and K. Wiithrich, /. Mol. Biol., 196, 611 (1987). Protein Structures in Solution by Nuclear Magnetic Resonance and Distance Geometry The Polypeptide Fold of the Basic Pancreatic Trypsin Inhibitor Determined Using Two Different Algorithms. DISGEO and DISMAN. 

The ability to trap disulfide-bonded intermediates in the folding pathway of bovine pancreatic trypsin inhibitor (BPTl) enabled Creighton to... 

Ecotin (eco) is a potent inhibitor of serine proteases that is derived from Escherichia coli. It was originally named for its ability to inhibit trypsin (E. coli trypsin inhibitor), but it is known to interact with and inhibit virtually all characterized tryp-sin-fold serine proteases. It is insensitive to the active site PI preference of the protease (the amino acid N-terminal to the cleaved or scissile bond ) and inhibits proteases with specificity towards basic, large hydrophobic, small aliphatic and acidic amino acids [2]. This remarkable breadth of inhibition classifies eco as a fold-specific inhibitor. It forms a unique tetrameric complex consisting of two protease molecules and two inhibitor molecules (the E2P2 complex), binding in a bi-dentate manner with two surface loop regions known as the primary and secondary sites (3) (Fig. 7.1). Eco itself is a 142 amino acid protein that forms a stable... 

J.P. Staley and P.S. Kim. 1990. Role of a subdomain in the folding of bovine pancreatic trypsin inhibitor TVatwre 344 685-688. (PubMed)... 

Five of the 6 tryptophan-NH resonances of lysozyme (mol. wt. 14400) in H2O are found at 10-12 ppm from DSS [33]. These protons take several hours to exchange with H when dissolved in H20. Their differential exchange rates and response to substrates are an aid to assignment. Eleven protons of bovine pancreatic trypsin inhibitor take more than 4 months to exchange with H in H20 at pH 7 [34,35]. Evidently some domains of this small protein (58 amino acids) are extremely tightly folded. 

Fernandez A, Kostov K, Berry RS (1999) From residue matching patterns to protein folding topographies General model and bovine pancreatic trypsin inhibitor. Proc Natl Acad Sci USA... 

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