Fourier-transform infrared spectroscopic study of Ca2+-binding to osteocalcin.
Osteocalcin, the gamma-carboxyglutamic acid-containing protein, which is the most abundant noncollagenous protein of bone and dentin, is considered to play roles in bone formation and remodeling. It is unclear how the gamma-carboxyglutamic acid side-chains in osteocalcin coordinate to Ca2+, since the X-ray structure of osteocalcin is not available. Interactions between Ca2+ and the gamma-carboxyglutamic acid side-chains in osteocalcin were investigated by Fourier-transform infrared spectroscopy. In the region of the antisymmetric stretches, the loss of intensity at 1574 cm(-1) and gain of intensity at 1600 cm(-1) were observed due to Ca2+-binding to osteocalcin. The spectral changes indicate that the gamma-carboxyglutamic acid side-chains in osteocalcin coordinate to Ca- in the malonate chelation mode, where a Ca2+ interacts with two oxygen atoms, one from each of the two COO- groups of a single gamma-carboxyglutamic acid residue. Addition of Ca2+ does not cause any spectral change in the spectra of decarboxylated osteocalcin since the gamma-carboxyglutamic acid residues are converted to the glutamic acid residues by chemical modification.
Mizuguchi
M
M
Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Japan.
Fujisawa
R
R
Nara
M
M
Nitta
K
K
Kawano
K
K
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D002417:Cattle; D008958:Models, Molecular; D015675:Osteocalcin / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D017550:Spectroscopy, Fourier Transform Infrared
D015675:Osteocalcin; D002118:Calcium