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Ca2+-specific fluorescence changes in N-dansylaminoethyl-labelled oncomodulin.
Canadian Journal of Biochemistry and Cell Biology = Revue Canadienne De Biochimie Et Biologie Cellulaire
|September 1, 1985
Summary
Rat oncomodulin exhibits a Ca2+-specific fluorescence change upon calcium binding, unlike carp parvalbumin. This indicates a significant molecular perturbation, even with a single calcium ion bound.
Area of Science:
- Biochemistry
- Molecular Biology
- Protein Chemistry
Background:
- Oncomodulin and parvalbumin are homologous calcium-binding proteins.
- Understanding calcium-binding dynamics is crucial for cellular signaling.
- Previous studies on parvalbumin show limited conformational changes upon ion binding.
Purpose of the Study:
- To investigate the Ca2+-binding properties of rat oncomodulin.
- To compare the Ca2+-induced conformational changes of oncomodulin with its homolog, carp parvalbumin.
- To characterize the Ca2+-specificity and extent of molecular perturbation in oncomodulin.
Main Methods:
- Chemical labeling of rat oncomodulin and carp parvalbumin at Cys-18 with N-dansylaziridine.
- Fluorescence spectroscopy to monitor changes in protein fluorescence upon metal ion binding.
- Titration experiments to determine the stoichiometry of Ca2+ binding and its effect on fluorescence.
Main Results:
- Dansyl fluorescence of labeled parvalbumin was unaffected by Mg2+ and Ca2+ binding.
- Ca2+ binding to labeled oncomodulin caused a ~20% quenching of dansyl fluorescence in the presence of Mg2+.
- The Ca2+-induced fluorescence quenching in oncomodulin was nearly complete at a 1:1 Ca2+/oncomodulin ratio, indicating high affinity and specificity for a single binding site.
Conclusions:
- Rat oncomodulin undergoes a significant Ca2+-specific conformational change, distinct from parvalbumin.
- This Ca2+-induced perturbation is detectable throughout the oncomodulin molecule.
- The findings suggest that oncomodulin's function may involve large, Ca2+-triggered molecular rearrangements.