Tyrosine sulfation is a common modification of many proteins, and the ability to phosphorylate tyrosine residues is an intrinsic property of many growth-factor receptors. In the present study, we have utilized the peptide hormone CCK8 (cholecystokinin), which occurs naturally in both sulfated and unsulfated forms, as a model to investigate the effect of tyrosine modification on metal-ion binding. The changes in absorbance and fluorescence emission on Fe3+ binding indicated that tyrosine sulfation or phosphorylation increased the stoichiometry from 1 to 2, without greatly affecting the affinity (0.6–2.8 μM at pH 6.5). Measurement of Ca2+ binding with a Ca2+-selective electrode revealed that phosphorylated CCK8 bound two Ca2+ ions. CCK8 and sulfated CCK8 each bound only one Ca2+ ion with lower affinity. Binding of Ca2+, Zn2+ or Bi3+ to phosphorylated CCK8 did not cause any change in absorbance, but substantially increased the change in absorbance on subsequent addition of Fe3+. The results of the present study demonstrate that tyrosine modification may increase the affinity of metal-ion binding to peptides, and imply that metal ions may directly regulate many signalling pathways.
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Research Article|
October 28 2008
Tyrosine modification enhances metal-ion binding
Graham S. Baldwin
;
Graham S. Baldwin
1
*The University of Melbourne Department of Surgery, Austin Health, Heidelberg, Victoria 3084, Australia
1To whom correspondence should be addressed (email grahamsb@unimelb.edu.au).
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Michael F. Bailey
;
Michael F. Bailey
†The Bio21 Institute, Parkville, Victoria 3010, Australia
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B. Philip Shehan
;
B. Philip Shehan
*The University of Melbourne Department of Surgery, Austin Health, Heidelberg, Victoria 3084, Australia
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Ioulia Sims
;
Ioulia Sims
*The University of Melbourne Department of Surgery, Austin Health, Heidelberg, Victoria 3084, Australia
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Raymond S. Norton
Raymond S. Norton
‡The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3050, Australia
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Biochem J (2008) 416 (1): 77–84.
Article history
Received:
May 29 2008
Revision Received:
July 14 2008
Accepted:
July 17 2008
Accepted Manuscript online:
July 17 2008
Citation
Graham S. Baldwin, Michael F. Bailey, B. Philip Shehan, Ioulia Sims, Raymond S. Norton; Tyrosine modification enhances metal-ion binding. Biochem J 15 November 2008; 416 (1): 77–84. doi: https://doi.org/10.1042/BJ20081059
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