Bovine pancreatic trypsine inhibitor folding

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. 

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 ... 

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

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... 

Formation of the correct disulfide pattern in proteins occurs concomitantly with acquisition of the correct folded form and it is driven by the thermodynamic stability of the native 3D structure. In the initial stages of protein folding processes thermodynamically stable local structures may play an important role (229-232). Thereby short range interactions are essentially implicated to promote stable core structures around which the rest of the protein chain will fold. These sequence-specific short range interactions may suffice for folding of isolated protein fragments Into stable native-like structures as well demonstrated with the bovine pancreatic trypsin inhibitor mono-cystinyl fragment 20-33/43-58 (233). 

D.P. Goldenberg, T.E. Creighton, Folding pathway of a circular form of bovine pancreatic trypsin inhibitor, J. Mol. Biol. 1984, 179, 527-545. 

Disulfide Bonds - Bonds between cysteine residues in a protein help to stabilize it once it has folded. Bovine pancreatic trypsin inhibitor (BPTI), which has 3 disulfide bonds in its 58 amino acid sequence, is one of the stablest proteins known. When the bonds are in place, it can be denatured at lOO C only in very acid solutions. Removing one disulfide bond reduces its resistance to thermal denaturation considerably. Removing all of the disulfide bonds causes it to unfold at room temperature. If time is allowed for refolding and the disulfide bonds are reformed, virtually 100% of the original activity of BPTI can be recovered, indicating that the sequence of amino acids contains enough information to properly reestablish the folding of the polypeptide. 

Staley JP, Kim PS (1994) Formation of a native-like subdomain in a partially folded intermediate of bovine pancreatic trypsin inhibitor. Protein Sci 3 1822-1832... 

Figure 1 shows the primary, secondary, and tertiary structures of the bovine pancreatic trypsin inhibitor (BPTI). This small protein is being widely used as a model for folding studies, because of its small size (58 amino acids), the fact that it contains both a-helical and (3-sheet structural elements, and its commercial availability. 

Bovine pancreatic trypsin inhibitor (BPTI), a small protein with 56 amino acid residues (Fig. 7), is the first one for which a detailed map of the refolding pathways was deciphered. The native state of BPTI contains three disulfide (S-S) bonds formed between six Cys residues. Native state is specified by [30-51 5-55 14—38] bonds. This notation indicates that Cys forms an S-S bond with Cys, and so on. Reduction of the S-S bonds unfolds BPTI. By using S-S bond formation as a progress variable, Creighton [79-83] devised ingenious methods to trap the disulfide-bonded intermediates along the folding pathway. 

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