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Related Experiment Videos

Dityrosine formation in calmodulin.

D A Malencik, S R Anderson

    Biochemistry
    |February 10, 1987
    PubMed
    Summary
    This summary is machine-generated.

    Ultraviolet irradiation of bovine calmodulin forms dityrosine, a fluorescent compound, impacting its calcium binding and biological activity. This photoproduct shows reduced interaction with calcium and impaired enzyme stimulation.

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    Area of Science:

    • Biochemistry
    • Photochemistry
    • Protein Chemistry

    Background:

    • Calmodulin (CaM) is a crucial calcium-binding protein involved in numerous cellular signaling pathways.
    • Ultraviolet (UV) irradiation can induce photochemical modifications in proteins, altering their structure and function.
    • Understanding these modifications is vital for interpreting experimental results and protein behavior under light exposure.

    Purpose of the Study:

    • To investigate the effects of 280-nm UV irradiation on bovine brain calmodulin.
    • To characterize the fluorescent photoproducts formed, specifically focusing on dityrosine formation.
    • To assess the impact of UV-induced modifications on calmodulin's calcium-binding properties and biological activity.

    Main Methods:

    • UV irradiation of calmodulin at 280 nm.

    Related Experiment Videos

  • Chromatographic separation (Ultrogel AcA 54, phenyl-agarose) of irradiated calmodulin.
  • Analysis of hydrolysates for dityrosine content.
  • Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).
  • Enzyme activity assays (p-nitrophenyl phosphatase) and protein-ligand binding studies (fluorescence titrations, myosin light chain kinase binding).

    • Main Results:

    • UV irradiation induced calcium-dependent changes in calmodulin's fluorescence, with decreased intrinsic tyrosine fluorescence and a new emission at 400 nm.
    • A specific fraction contained dityrosine, a cross-linked tyrosine derivative, suggesting intramolecular cross-linking of Tyr-99 and Tyr-138.
    • The dityrosine-containing photoproduct exhibited weakened calcium binding and was unable to stimulate calcineurin activity.
    • Binding affinity for smooth muscle myosin light chain kinase was significantly reduced.

    Conclusions:

    • 280-nm UV irradiation of calmodulin leads to intramolecular dityrosine formation, altering its functional properties.
    • The dityrosine photoproduct demonstrates impaired calcium-dependent signaling capabilities.
    • Metal ions like Cd2+ can promote dityrosine formation, while Mn2+, Cu2+, and antioxidants inhibit it.