The effect of genetically engineered spider silk-dentin matrix protein 1 chimeric protein on hydroxyapatite nucleation

Spider silks exhibit remarkable mechanical properties while dentin matrix protein 1 provides controlled nucleation and hydroxyapatite growth. In the present work, these two attributes were combined via genetic engineering to form a chimera, a clone encoding consensus repeats from the major protein in the spider dragline silk of Nephila clavipes fused to the carboxyl terminal domain of dentin matrix protein 1 (CDMP1). The objective was to exploit the self-assembly and material properties of silk proteins with controlled hydroxyapatite (HA) formation from CDMP1, for novel biomaterial composites. The purified recombinant protein retained native-silk like self-assembly properties and β-sheet structure when formed into films and treated with methanol. When the chimeric protein in solution was incubated with CaCl2, the secondary structure shifted from random coil to α-helix and β-sheet, due to the interactions between the CDMP1 domain and Ca2+. The control protein without the CDMP1 domain did not undergo a similar transition. Films formed from the recombinant protein were mineralized using simulated body fluids and induced the formation of calcium-deficient carbonated HA, Ca10(PO4)6(OH)2 based on SEM, EDS, FTIR and TEM analysis. This mineral phase was not formed on the films formed from the control spider silk protein without the CDMP1 domain. Considering the osteoconductivity of HA and the novel material features of spider silks, these new hybrid systems offer potential as biomaterials for a number of potential applications.