1996 Volume 72 Issue 5 Pages 104-107
Bromelain inhibitor VI from pineapple stem (BI-VI) is a unique double-chain cysteine proteinase inhibitor composed of an 11-residue light chain and a 41-residue heavy chain linked by disulfide bonds. The positions of six of the ten half cystines in the primary structure of BI-VI resemble those of the six half cystines in bovine pancreatic trypsin inhibitor (BPTI), a serine proteinase inhibitor which apparently shares some properties with BI-VI. These facts suggested that they might resemble in their three-dimensional structures. To clarify this point, the solution structure of BI-VI was elucidated using nuclear magnetic resonance spectroscopy and simulated annealing-based calculations. Thus, the inhibitor was shown to be composed of two distinct domains, each constructed by a three-stranded antiparallel β-sheet. Comparison with BPTI revealed conclusively that BI-VI is distinctly different in three-dimensional structure from BPTI.