AN NMR-BASED IDENTIFICATION OF PEPTIDE-FRAGMENTS MIMICKING THE INTERACTIONS OF THE CATHEPSIN-B PROPEPTIDE

Selected fragments of the 62-residue proregion (or residues 1p-62p) of the cysteine protease cathepsin B were synthesized and their interact ions with cathepsin B studied by use of proton NMR spectroscopy. Pepti de fragments 16p-51p and 26p-51p exhibited differential perturbations of their proton resonances in the presence of cathepsin B, These reson ance perturbations were lost for the further truncated 36p-51p fragmen t, but remained in the 26p-43p and 28p-43p peptide fragments. Residues 23p-26p or TWQ(25)A in the N-terminal 1p-29p fragment did not show ca thepsin B-induced resonance perturbations although the same residues h ad strongly perturbed proton resonances within the 16p-51p peptide. Bo th the 1p-29p and 36p-51p fragments lack a common set of hydrophobic r esidues 30p-35p or (FYNVDI35)-Y-30 from the proregion, The presence of residues (FYNVDI35)-Y-30 appears to confer a conformational preferenc e in peptide fragments 16p-51p, 26p51p, 28p-43p and 26p-43p, but the s ame residues induce the aggregation of peptides 16p-36p and 1p-36p, Th e peptide fragment 26p-43p binds to the active site, as indicated by i ts inhibition of the catalytic activity of cathepsin B, The cathepsin B prosegment can therefore be reduced into smaller, but functional sub units 28p-43p or 26p-43p that retain specific binding interactions wit h cathepsin B, These results also suggest that residues (FYNVDI35)-Y-3 0 may constitute an essential element for the selective inhibition of cathepsin B by the full-length cathepsin B proregion, (C) 1998 Federat ion of European Biochemical Societies.