Binds tightly to hydroxyapatite. Appears to form an integral part of the mineralized matrix. Probably important to cell-matrix interaction. Promotes Arg-Gly-Asp-dependent cell attachment. N-glycosylated; glycans consist of sialylated and core-fucosylated bi-, tri- and tetraantennary chains. O-glycosylated at eight sites; mucin-type glycans contain Gal, GlcNAc, GalNAc and terminal NeuAc. Sulfated on either Tyr-313 or Tyr-314. It is possible that the segments of clustered carboxyl groups mediate the strong binding to hydroxyapatite.