Biomedical Engineering Reference
In-Depth Information
proteins, as well as recombinant rat osteopontin (rOPN) lacking phosphate residues,
were compared. All three OPN proteins adsorbed to the edge of the (100) and
(121) surfaces of the COM crystals. However, only the mOPN and bOPN changed
the crystal morphology to a dumbbell shape. The rOPN lacked this morphological
transforming ability.
The attachment of mOPN and bOPN to the COM crystal surface was investigated
in detail [
62
]. The adsorption of mOPN was more specific to the (100) surface. Since
the (100) surface of COM is the richest surface in terms of calcium atoms [
63
],
Langdon concluded, on the basis of the electrostatic interaction between phosphate
residues of OPN and calcium ions on the crystal surface, that the adsorption of
phosphorylated OPN is not due to the specific structure defined by the amino acid
sequence but to a non-specific interaction [
62
].
The interaction of amelogenin to a specific crystal surface of OCP has been
studied [
64
,
65
] and is described in Chap. 5.
4.6
Controlling Transformation
He et al. examined the change in the mineral phase during HAP formation with
DMP1 and identified the peptide sequences in DMP1 particularly important for
HAP crystal formation. When DMP1 adsorbed to a glass plate was placed in a
calcium phosphate solution, ACP precipitated on the glass plate and then trans-
formed into HAP. In a control experiment with bovine serum albumin adsorbed to
the glass plate, HAP crystal formation was not observed under the same conditions
although a small amount of ACP precipitated. He et al. further found that HAP
crystal formation accelerated when two peptides derived from DMP1 (ESQES
and QESQSEQDS) were adsorbed to the glass plate, as seen with DMP1 [
39
].
However, the mechanism of HAP crystal formation promoted by the protein or
peptides was not determined. Tsuji et al. used the same two peptides and applied
the experiments to elucidate the mechanism of HAP crystal formation promoted by
proteins containing the peptide sequences [
66
].
The time-resolved static light scattering (TR-SLS) measurement technique
developed by Onuma et al. is an excellent method for analyzing the crystallization
of small particles freely diffused in solution [
67
]. This technique enables real-time
analysis of the apparent molecular mass, gyration radius, and fractal dimension
(an index of the inner structure ordering) of calcium phosphate particles. However,
although DMP1 and peptides ESQES and QESQSEQDS accelerate crystal forma-
tion when they are adsorbed to insoluble matrices such as collagen or a glass plate
[
38
,
39
], they do not accelerate crystal formation when they are present in a free
form [
40
]. Thus, the mechanism of HAP crystal formation induced by DMP1 and
these peptides cannot be analyzed using TR-SLS measurement.
Therefore, an attempt was made to synthesize proteins that can accelerate HAP
crystal formation without immobilization. In general, there are strict limitations
on the design and production of proteins with a desired function using only
