Reduced bovine pancreatic trypsin inhibitor has a compact structure.
The conformation of reduced bovine pancreatic trypsin inhibitor (R-BPTI) under reducing conditions was monitored by measurements of nonradiative excitation energy-transfer efficiencies (E) between a donor probe attached to the N-terminal Arg1 residue and an acceptor attached to one of the lysine residues (15, 26, 41, or 46) [Amir, D., & Haas, E. (1987) Biochemistry 26, 2162-2175]. High-excitation energy-transfer efficiencies that approach those found in the native state were obtained for the reduced labeled BPTI derivatives in 0.5 M guanidine hydrochloride (Gdn.HCl) and 4 mM DTT. Unlike the dependence expected for a random coil chain, E does not decrease as a function of the number of residues between the labeled sites. The efficiency of energy transfer between probes attached to residues 1 and 15 in the reduced state is higher than that found for the same pair of sites in the native state or reduced unfolded (in 6 M Gdn.HCl) state. This segment also shows high dynamic flexibility. These results indicate that the overall structure of reduced BPTI under folding (but still reducing) conditions shows a high population of conformers with interprobe distances similar to those of the native state. Reduced BPTI seems to be in a molten globule state characterized by a flexible, compact structure, which probably reorganizes into the native structure when the folding is allowed to proceed under oxidizing conditions.
Amir
D
D
Department of Life Science, Bar-Ilan University, Ramat Gan, Israel.
Haas
E
E
D007611:Aprotinin; D004220:Disulfides; D004229:Dithiothreitol; D004492:Edetic Acid; D004735:Energy Transfer; D019791:Guanidine; D006146:Guanidines; D010084:Oxidation-Reduction; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D014361:Trypsin Inhibitors
D004220:Disulfides; D006146:Guanidines; D014361:Trypsin Inhibitors; D007611:Aprotinin; D004492:Edetic Acid; D019791:Guanidine; D004229:Dithiothreitol