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4-(Fluoromethyl)phenyl phosphate acts as a mechanism-based inhibitor of calcineurin
T L Born1, J K Myers, T S Widlanski
1Department of Biochemistry and Molecular Biology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA.
Abstract:
The compound 4-(fluoromethyl)phenyl phosphate (FMPP), recently shown to be a mechanism-based inhibitor of prostatic acid phosphatase (Myers, J.K., and Widlanski, T.S. (1993) Science 262, 1451-1453), was examined for its effect on calcineurin. This compound inhibits calcineurin in a time-dependent, first order manner. Inactivation with [3H]FMPP led to a specific labeling of the catalytic subunit with a stoichiometry of 0.75 mol of label/mol of protein. A related substrate, 4-methylphenyl phosphate, is able to protect calcineurin from FMPP-mediated inhibition. Scavenging nucleophiles, such as cysteine, do not affect the rate of inhibition when included in the reaction. In addition, extensive dialysis indicates that inhibition is essentially irreversible. These results demonstrate that FMPP inactivates calcineurin in a mechanism-based fashion by forming a covalent adduct with calcineurin A, the catalytic subunit.
Insights
The enzyme calcineurin is inactivated by 4-(fluoromethyl)phenyl phosphate (FMPP) through a time-dependent, irreversible mechanism. FMPP forms a covalent bond with calcineurin A, the catalytic subunit.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Prostatic acid phosphatase (PAP) is a key enzyme in prostate cancer.
- Mechanism-based inhibitors are crucial tools for studying enzyme function.
- Calcineurin is a critical calcium-dependent phosphatase involved in immune response and T-cell activation.
Purpose of the Study:
- To investigate the effect of 4-(fluoromethyl)phenyl phosphate (FMPP) on calcineurin activity.
- To elucidate the mechanism by which FMPP interacts with calcineurin.
Main Methods:
- Enzyme inhibition assays were performed using FMPP and calcineurin.
- Time-dependent inactivation kinetics were analyzed.
- [3H]-labeled FMPP was used to identify the binding site and stoichiometry of inhibition.
- Protection assays with a related substrate (4-methylphenyl phosphate) were conducted.
- Scavenging nucleophiles (e.g., cysteine) were used to assess the reaction mechanism.
Main Results:
- FMPP inhibits calcineurin in a time-dependent, first-order manner.
- Specific labeling of the catalytic subunit (calcineurin A) with [3H]FMPP occurred at a stoichiometry of 0.75 mol/mol protein.
- The substrate 4-methylphenyl phosphate protected calcineurin from FMPP inhibition.
- Inhibition was irreversible, as indicated by extensive dialysis.
- Scavenging nucleophiles did not alter the inhibition rate, suggesting a non-nucleophilic attack mechanism.
Conclusions:
- FMPP acts as a mechanism-based inactivator of calcineurin.
- FMPP forms an irreversible covalent adduct with the catalytic subunit of calcineurin (calcineurin A).
- This study provides insights into the structure-activity relationship of calcineurin inhibitors.