pH dependence studies provide insight into the structure and mechanism of thimet oligopeptidase (EC 3.4.24.15)

Authors :: Sigman, Jeffrey A.
Edwards, Sarah R.
Pabon, Amanda
Glucksman, Marc J.
Wolfson, Adele J.
Source :: FEBS Letters; Jun2003, Vol. 545 Issue 2/3, p224, 5p
Publication Year :: 2003
Abstract: Thimet oligopeptidase (EC 3.4.24.15; TOP) is a Zn(II) endopeptidase implicated in physiological regulation of processes involving neuropeptides. The present study clarifies the active site structure and mechanism of catalysis of TOP. The enzyme exhibited a bell-shaped pH dependence of activity having an acidic limb due to a protonation event with a pK<subscript>a</subscript> of 5.7 and a basic limb with pK<subscript>a</subscript> of 8.8. The acidic limb can be attributed to protonation of a residue affecting k<subscript>cat</subscript> while the alkaline limb may be due to conformational change. Mutation of Tyr612 to Phe resulted in more than 400-fold decrease in activity. This result, supported by modeling studies, implicates Tyr612 in transition state stabilization analogous to the role of His231 of thermolysin. [Copyright &y& Elsevier]

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