Calcium and phosphorylation double-regulating caltractin initiating target protein XPC function.

Human centrin 2 (HsCen2) is a member of the EF-hand protein that plays a critical role in the centrosome duplication and separation during cell division. Reversible protein phosphorylation is an important regulatory mechanism for centrin. To obtain insight into the structural basis for the functional effects of phosphorylation, it was verified that the serine residue at position 170 of HsCen2 can be phosphorylated by protein kinase A using ³¹P NMR spectroscopy. While the protein was phosphorylated, the extents of α-helix and the exposed hydrophobic surfaces on HsCen2 were decreased significantly. In the present paper, we reported the regulation and control of peptide p22-XPC binding with HsCen2 by isothermal titration calorimetry (ITC) and spectra. After being phosphorylated, the affinity of p22-XPC with HsCen2 was weakened almost 2 orders of magnitudes. And removing calcium ions from the system, no significant binding between them has been observed. Their binding was reversible. Functions of XPC may be double-regulated and controlled by calcium ions as well as phosphorylation. These results are of significance for understanding the relationship between PTM and metal regulation.

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