IBSP and cancer: These polyglutamic acid-rich regions25 are implicated in osteoblast differentiation,31 mineralisation,27,31 and may influence osteoclast activity.32 In rat and porcine BSP, these domains nucleate and bind HA.33–36 Specifically, in porcine BSP, residues 42–125 and 133–272 can nucleate HA independent of the intact protein structure.37 The C-terminal domain contains the RGD motif,9 a key regulator of cell chemotaxis and integrin-mediated signalling,38,39 which is involved in skeletal biology and cancer.