Synthesis and kinetic characterization of hyperbolic inhibitors of human cathepsins K and S based on a succinimide scaffold

Kinetic Characterization of Cerium and Gallium Ions as Inhibitors of Cysteine Cathepsins L, K, and S

“…The kinetic mechanisms for the interaction with cathepsins K and S were diagnosed as hyperbolic mixed inhibition, trending towards activation at high substrate concentrations. Similar mechanisms were previously diagnosed for small molecule modifiers of cathepsins K and S, which presumably act through allosteric mechanisms [ 43 , 44 , 45 ], suggesting that this is a common mechanism by which these peptidases may be regulated by chemically diverse modifiers. Furthermore, the affinity of Ga 3+ ions for cathepsin L was one order of magnitude higher than for the remaining two ( K X values of 6 × 10 −7 M for cathepsin L versus ~4 × 10 −6 M for cathepsins K and S).…”

“…Cathepsins K and S are more closely related to each other than to cathepsin L [ 1 ], but all three have similar substrate specificity [ 42 ]. This finding does, however, complement the fact that hyperbolic inhibitors have been described for cathepsins K and S [ 43 , 44 , 45 ], whereas no such inhibitors are known for cathepsin L. It is possible that cathepsin L is incapable of such modification due to a much more limited activity space, although it has a similar conformational space to cathepsins K and S [ 58 ]. Therefore, an allosteric mode of action of Ce 3+ , Ce 4+ , and Ga 3+ ions cannot be excluded and possibly involves interactions of Ce 3+ ions with multiple sites on cathepsins K and S, as discussed in Section 2.2…”

“…Powdered bovine neck ligament elastin was from the Elastin Products Company, Inc. (Owensville, MO, USA). Recombinant human cathepsins L, K, and S were produced as zymogens in E. coli and activated in vitro, as described previously [ 45 , 64 ]. Active enzyme concentrations were determined by active site titration with the irreversible inhibitor E-64 (Bachem, Bubendorf, Switzerland).…”

Regulation of Peptidase Activity beyond the Active Site in Human Health and Disease

“…However, with partial inhibition, we can maintain the basic activity required for homeostasis. Partial (hyperbolic) inhibition mechanisms were described for allosteric effectors of cathepsin K NSC1334 and NSC94914 [202,203] as well as putative such modifiers of cathepsin K and cathepsin S [203,232]. Several of them, including NSC13345 and NSC94914, showed peculiar kinetic profiles of inhibition and/or activation, depending on the concentration of the substrate [202,203], and altogether, a diverse spectrum of effects ranging from partial specific to partial catalytic inhibition have been observed [203].…”