초록/요약

There are four EF-hand polypeptides in calmodulin, a natural ubiquitous calcium binding protein that activates the enzymes involved in Ca2+-mediated signal transduction. An EF-hand polypeptide has six carboxylate functional groups in the middle loop region between two rigid polypeptides. In this study, a calcium binding polymer (CBP) with a structure of poly(L-alanine)-poly(L-alanine-co-L-glutamic acid)-poly(ethylene glycol)-poly(L-alanine-co-L-glutamic acid)-poly(L-alanine) (PA-PAE-PEG-PAE-PA; A11.1-A3.4E3.2-EG40.1-A3.4E3.2-A11.1) was synthesized by mimicking the EF-hand polypeptide. The 6-7 carboxylate functional groups from PAE are expected to form a binding site for Ca2+. As the Ca2+ bound to CBP, small changes in the circular dichroism spectra and 13C NMR spectra were observed, indicating that Ca2+ binding to CBP induced changes in the conformation of CBP. The binding constant of CBP to Ca2+ was investigated by using the competitive binding of 2,2′, 2″, 2⌄ -{ethane-1,2-diylbis[oxy(4-bromo-2,1-phenylene)nitrilo]} tetraacetic acid (5,5-Br2-BAPTA). The binding constant obtained with a CaLigator program by least-squares fitting of the absorbance profile as a function of Ca2+ concentration was 5.1 × 105 M-1, which was similar to that of calmodulin. The selectivity of CBP for metal ion binding was compared among Ca2+, Cu2+, and Zn2+. The binding constant was obtained through a similar competitive binding study with murexide. The binding constants for Ca2+, Cu2+, and Zn2+ were 7.0 × 105, 4.2 × 105, and 1.7 × 105 M-1, respectively, indicating 2-4-fold higher selectivity of CBP for Ca2+ compared to Cu2+ and Zn2+. The CBP has selectivity for Ca2+, and binding affinity for Ca2+ was similar to the biological Ca2+ binding motif of calmodulin. (Figure Presented). © 2016 American Chemical Society.