Practice question

Metalloprotease class distinguished by requirement zinc ion for catalytic mechanism and often calcium for structural integrity. Active site contains conserved motif HEXXH where histidines coordinate zinc plus third ligand histidine or glutamate forming tetrahedral geometry polarizing water molecule held nearby as hydroxide ion via general base glutamate abstracting proton making hydroxide nucleophile that attacks peptide carbonyl carbon forming tetrahedral transition state stabilized by zinc positive charge and nearby tyrosine oxyanion hole. Removal of zinc abolishes activity irreversibly. Ethylenediaminetetraacetic acid EDTA is hexadentate aminopolycarboxylate chelator with four carboxylate oxygen and two amine nitrogen electron pair donors wrapping divalent cation forming octahedral complex extremely stable formation constants log Kf Zn2+ sixteen point five, Ca2+ ten point seven, Mg2+ eight point seven at pH eight. Chelation strips Zn2+ from catalytic site and removes Ca2+ bridging extracellular cadherin domains or stabilizing metalloprotease beta propeller. This mechanistic insight supports diagnostic and therapeutic applications while reinforcing core immunological and cell biology principles taught in advanced curricula.