Hyun Ik Park and Li-June Ming*
Department of Chemistry and
Institute for Biomolecular Science
University of South Florida
Tampa, Florida 33620-5250

Running title:  Mechanistic Role of the Coordinated Tyr in Astacin
Key words:  astacin, metalloprotease, NMR, Co(II), Cu(II)

Abstract
    Crayfish astacin belongs to the only Zn protein family containing a coordinated Tyr ligand in the active site, and is a rare example of Zn enzymes whose activity can be significantly restored by Cu²⁺.  The highly active Co²⁺ and Cu²⁺ derivatives of astacin can serve as good models of the native enzyme for structural and mechanistic studies by means of optical and magnetic resonance techniques.  Upon the introduction of the inhibitor Tyr-hydroxamate to these two metal derivatives of astacin, the coordinated Tyr in the active site is detached based on our optical and NMR studies in solution.  The significance of the detachment of the coordinated Tyr in the action of astacin is four-fold:  (1) to enhance the Lewis acidity of the active site metal, (2) to balance the negative charge of the transition state gem-diolate-enzyme complex, (3) to relieve the steric crowding upon substrate binding, and (4) to stabilize the enzyme-substrate complex by way of a H-bonding.

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(Read an introduction about astacin, or about aminopeptidase)

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