Native protein structures bovine pancreatic trypsin inhibitor

The stress-70 proteins interact with a broad spectrum of polypeptide substrates, but they have some degree of specificity in their interactions. In several instances, it has been shown that a stress-70 protein can bind to proteins [e.g., bovine pancreatic trypsin inhibitor (BPTI), a-lactalbumin] that have been stabilized in a nonnative, or denatured, form by reduction and carboxymethylation of the cysteines that would normally form disulfides at the same time, they will not bind to the native forms of the same proteins (Liberek et al., 1991b Palleros et ai, 1991, 1992). This suggests that the peptide-binding activity of the stress-70 proteins discriminates in favor of polypeptides in a denatured, and possibly extended, conformation over those in a compact secondary and tertiary structure. NMR experiments demonstrating that the E. coli dnaK... 

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). 

Figure 6.28 shows the amino acid sequence of bovine pancreatic trypsin inhibitor (BPTI). More importantly. Figure 6.28 compares the secondary structures observed in the native protein and predicted by the Chou-Fasman rules. Note that exceptionally good agreement is found between the predicted and observed structures. 

Bovine pancreatic trypsin inhibitor (BPTI) has been a widely used model protein for study. There is a good deal of both experiment and computational study on this system. There are a number of crystal and NMR structures of the native, oxidized form of BPTI. The protein with the disulfide linkage reduced, an presumably unfolded state, has been the subject of a number of experimental studies and previous simulations in our group. ... 

Raman spectroscopy is not yet commonly used to follow conformational variations of proteins. Only a few reports are available. Brunner and Sussner (1972) and Brunner and co-workers (1974) studied the thermal denaturation of bovine pancreatic trypsin inhibitor (BPTI) with Cys 14-Cys 38 bond reduced and with this reduced molecule then carboxamidomethylated. The native molecule was first analyzed. The amide I band at 1664 cm which is characteristic of p structure indicates that this structure is dominant in the molecule. The amide III band displays three well resolved peaks at 1243, 1265, and 1288 cmwhich are characteristic of antiparallel P sheets, random coil, and a helical structures. From these data Brunner and Sussner (1972) and Brunner and co-workers (1974) evaluated the content of secondary structures to be ca. 45% P structure, 30% random coil, and 25% a helix this is in satisfactory agreement with the X-ray data. 

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