Two‐dimensional 1H NMR of two chemically modified analogs of the basic pancreatic trypsin inhibitor

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Abstract
Two-dimensional NMR was used to obtain sequence specific assignments for the 1H NMR spectra of 2 chemically modified analogs of the basic pancreatic trypsin inhibitor. In 1 analog the disulfide bond 14-38 was cleaved, in the 2nd-derivative the N-terminus was transaminated. From measurements of the chemical shifts and determination of the sequence locations of slowly exchanging backbone amide protons it was found that conformational differences between the native inhibitor and the chemical modifications occur exclusively near the modification sites and that the internal H- bonds are nearly fully preserved. Intriguing conformation differences with respect to the native protein are that for 5 residues in the transaminated inhibitor and for 1 residue in the reduced inhibitor multiple local conformers are indicated, and that the 4 internal water molecules observed in the crystal structure of the native inhibitor appear not to be preserved after reduction of the disulfide bond 14-38.

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