Recombinant hBMP4 incorporated with non-canonical amino acid for binding to hydroxyapatite

A novel growth factor containing non-canonical amino acids was designed and synthesized to enhance the binding to hydroxyapatite (HA). The designed protein was human bone morphogenetic protein 4 (hBMP4) incorporating diphosporylated serines (pSpS) that was found in salivary protein statherin and was reported to be responsible for binding to HA. Recombinant hBMP4 and a short peptide sequences containing pSpS were ligated by enzymatice reaction of sortase A, which exchanges the terminal amino acids of two polypeptides. Resulting hBMP4 containing pSpS (hBMP4-pSpS) bound HA more efficiently than hBMP-4 tagged with canonical serines (hBMP4-SS). The HA-bound hBMP-4-pSpS exhibited osteogenesis inducing activity to multipotential mesenchyme cells (C3H10T1/2) as evidenced by increased expression of osteogenic markers, which was not seen by hBMP4-SS. This novel protein with non-canonical serines will be applicable to bone regeneration materials in combination with HA.