muramidase and carbobenzoxy-leucyl-leucyl-norvalinal

Cell-permeant peptidyl aldehydes and diazomethylketones are frequently utilized as inhibitors of regulatory intracellular proteases. In the present study the specificities of several peptidyl inhibitors for purified human mu-calpain and 20 S proteasome were investigated. Acetyl-LLnL aldehyde, acetyl-LLM aldehyde, carbobenzyloxy-LLnV aldehyde (ZLLnVal), and carbobenzyloxy-LLY-diazomethyl ketone produced half-maximum inhibition of the caseinolytic activity of mu-calpain at concentrations of 1-5 x 10(-7) M. In contrast, only ZLLnVal was a reasonably potent inhibitor of the caseinolytic activity of 20 S proteasome, producing 50% inhibition at 10(-5) M. The other inhibitors were at least 10-fold less potent, producing substantial inhibition only at near saturating concentrations in the assay buffer. Further studies with ZLLnVal demonstrated that its inhibition of the proteasome was independent of casein concentration over a 25-fold range. Proteolysis of calpastatin or lysozyme by the proteasome was half-maximally inhibited by 4 and 22 microM ZLLnVal, respectively. Thus, while other studies have shown that ZLLnVal is a potent inhibitor of the hydrophobic peptidase activity of the proteasome, it appears to be a much weaker inhibitor of its proteinase activity. The ability of the cell permeant peptidyl inhibitors to inhibit growth of the yeast Saccharomyces cerevisiae was studied because this organism expresses proteasome but not calpains. Concentrations of ZLLnVal as high as 200 microM had no detectable effect on growth rates of overnight cultures. However, yeast cell lysates prepared from these cultures contained 2 microM ZLLnVal, an amount which should have been sufficient to fully inhibit hydrophobic peptidase activity of yeast proteasome. Degradation of ubiquitinylated proteins in yeast extracts by endogenous proteasome was likewise sensitive only to high concentrations of ZLLnVal. The higher sensitivity of the proteinase activity of calpains to inhibition by the cell permeant inhibitors suggests that calpain-like activities may be targets of these inhibitors in animal cells.

Topics: Acetylcysteine; Calcium-Binding Proteins; Calpain; Catalysis; Cysteine Endopeptidases; Cysteine Proteinase Inhibitors; Diazomethane; Enzyme Precursors; Humans; Kinetics; Leupeptins; Multienzyme Complexes; Muramidase; Oligopeptides; Plant Proteins; Protease Inhibitors; Proteasome Endopeptidase Complex; Saccharomyces cerevisiae; Serine Proteinase Inhibitors; Ubiquitins

We have studied whether various agents that inhibit purified yeast and mammalian 26 S proteasome can suppress the breakdown of different classes of proteins in Saccharomyces cerevisiae. The degradation of short-lived proteins was inhibited reversibly by peptide aldehyde inhibitors of proteasomes, carbobenzoxyl-leucinyl-leucinyl-leucinal (MG132) and carbobenzoxyl-leucinyl-leucinyl-norvalinal (MG115), in a yeast mutant with enhanced permeability, but not in wild-type strains. Lactacystin, an irreversible proteasome inhibitor, had no effect, but the beta-lactone derivative of lactacystin, which directly reacts with proteasomes, inhibited the degradation of short-lived proteins. These inhibitors also blocked the rapid ubiquitin-dependent breakdown of a beta-galactosidase fusion protein and caused accumulation of enzymatically active molecules in cells. The degradation of the bulk of cell proteins, which are long-lived molecules, was not blocked by proteasome inhibitors, but could be blocked by phenylmethylsulfonyl fluoride. This agent, which inhibits multiple vacuolar proteases, did not affect the proteasome or breakdown of short-lived proteins. These two classes of inhibitors can thus be used to distinguish the cytosolic and vacuolar proteolytic pathways and to increase the cellular content of short-lived proteins.

Topics: Acetylcysteine; Animals; Kinetics; Leupeptins; Mammals; Muramidase; Peptide Hydrolases; Protease Inhibitors; Proteasome Endopeptidase Complex; Saccharomyces cerevisiae; Substrate Specificity; Ubiquitins; Vacuoles