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Related Experiment Videos

Crystal structure of a papain-E-64 complex.

K I Varughese1, F R Ahmed, P R Carey

  • 1Division of Biological Sciences, National Research Council of Canada, Ottawa, Ontario.

Biochemistry
|February 7, 1989
PubMed
Summary
This summary is machine-generated.

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E-64, an irreversible cysteine protease inhibitor, forms a covalent bond with papain

Area of Science:

  • Biochemistry
  • Structural Biology

Background:

  • Papain is a cysteine protease implicated in various biological processes.
  • E-64 is a known irreversible inhibitor of cysteine proteases.
  • Understanding the precise mechanism of papain inhibition by E-64 is crucial for protease research.

Purpose of the Study:

  • To elucidate the structural basis of papain inactivation by the cysteine protease inhibitor E-64.
  • To determine the binding interactions between papain and E-64 at the atomic level.
  • To clarify the roles of active site residues and subsites in the inhibition process.

Main Methods:

  • Crystallization of the papain-E-64 complex using the hanging drop method.
  • X-ray diffraction analysis to determine the three-dimensional structure of the complex.

Related Experiment Videos

  • Molecular replacement and difference electron density map analysis for structure solution and inhibitor fitting.
  • Refinement of the complex structure to R = 23.3% at 2.4-A resolution.

    • Main Results:

    • The papain-E-64 complex was crystallized in space group P212121.
    • A covalent bond was identified between the active-site cysteine 25 of papain and the C-2 atom of E-64.
    • The E-64 inhibitor was found to interact with the S subsites of papain, contrary to previous hypotheses.
    • Papain's histidine 159 was determined to play a binding role, not a catalytic one, in the inactivation.

    Conclusions:

    • The crystal structure reveals the detailed atomic interactions of E-64 with papain.
    • The findings clarify the binding mode of E-64, highlighting interactions with S subsites.
    • The study redefines the role of histidine 159 in papain inactivation by E-64.