Sequence-Specific 1H NMR Assignments and Determination of the Secondary Structure for the Activation Domain Isolated from Pancreatic Procarboxypeptidase B

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Abstract
Nearly complete sequence-specific 1H NMR assignments are presented for amino acid residues 3-81 in the 81-residue globular activation domain of porcine pancreatic procarboxypeptidase B isolated after limited tryptic proteolysis of the zymogen. These resonance assignments are consistent with the chemically determined amino acid sequence. Regular secondary structure elements were identified from nuclear Overhauser effects and the sequence locations of slowly exchanging blackbone amide protons. The molecule contains two .alpha.-helices, including resides 20-30 and approximately residues 58-72, and a three-stranded antiparallel .beta.-sheet with the individual strands extending approximately from 12 to 17, 50 to 55 and 75 to 77. The identification of these secondary structures and a preliminary analysis of additional long-range NOE distance constraints show that isolated activation domain B forms a stable structure with the typical traits of a globular protein. The data presented here are the basis for the determination of the complete three-dimesional structure of activation domain B, which is currently in progress.