Plasma‐sprayed coatings in the system CaO‐TiO2‐ZrO2‐P2O5 for long‐term stable endoprostheses

Bioceramic materials based on CaTiZr₃(PO₄)₆ were synthesised by a ceramic route, characterised by XRD and EMPA analyses, and used as a precursor material to coat Ti6Al4V substrates by atmospheric plasma spraying. This led to multiphase bioactive layers with sufficient porosity for medical applications. In‐vitro biocompatibility tests conducted with primary cultures of rat bone marrow cells incubated for two weeks showed that the CaTiZr₃(PO₄)₆ substrates supported a distinctly higher cell growth rate compared with Thermanox™ cell cover slips used as a control.     

Modelling of Protein‐Protein Interactions of Bone Morphogenetic Protein‐2 (BMP‐2) by 3D‐Rapid Prototyping

Recently we were able to apply the technique of 3D‐Rapid Prototyping (3D‐RP) to the construction of highly accurate three‐dimensional plastic models of biomolecules [Laub, M. et al. (2001), Materialwiss. Werkstofftech. 32, 926]. These models are derived from x‐ray crystallographic data and therefore represent exact replicas of the depicted molecules. Due to their accuracy these models should be suitable for the modelling of protein‐protein‐interactions. In a first study using 3D‐Rapid Prototyping models of bone morphogenetic protein‐2 (BMP‐2) we were able to identify a novel structural motive on the concave side of this protein which we termed anthelix since a left‐handed helix (radius ca. 0.8–1 nm, pitch 8–9 nm) can be fitted into this groove. Based on these structural findings we identified a 15mer polypeptide (KNMTPYRSPPPYVPP) from the Brookhaven database as a potential physiological ligand. Molecular docking studies using a geometric recognition approach confirmed the anthelix as a possible binding site for this peptide. However in affinity chromatography experiments no binding between BMP‐2 and the immobilized peptide was observed. As the question arose whether 3D‐Rapid Prototyping is in general suitable for modelling protein‐protein interaction we used dimeric BMP‐2 to study exemplary monomer‐dimer interaction. Molecular docking studies using the monomeric BMP‐2 subunits predicted a structure which is nearly identical to that found in dimeric BMP‐2 (root mean square deviation < 1 Å) proving the suitability of geometric docking. 3D‐RP‐BMP‐2‐monomers (size 140 mm × 75 mm × 65; magnification ca. 22 × 10⁶ fold) constructed from dimeric BMP‐2 could be assembled by hand yielding a structure highly homologous to dimeric BMP‐2. Differences between the 3D‐Rapid Prototyping model of dimeric BMP‐2 and the assembled monomers arose in several gaps at the interface between the two monomers which are not visible in the dimeric structure. These gaps can be explained by the way the solvent‐accessible molecular surface is generated. During this process an exterior probe sphere is rolled over the spherical atoms of the molecule. Distances between the monomers smaller than the diameter of this sphere are bridged thus resulting in a coherent surface. We conclude that 3D‐Rapid Prototyping is in general eligible for the modelling of protein‐protein‐interaction though there are further efforts needed to increase our understanding of this process.     

Molecular Modelling of Bone Morphogenetic Protein‐2 (BMP‐2) by 3D‐Rapid Prototyping

Bone morphogenetic proteins (BMP) play a decisive role in bone development and osteogenesis. In the past they have been the subject of widespread research and clinical trials as stimulants of bone growth. Recently BMP‐2 has been chemically immobilized on implant surfaces leading to enhanced bone growth and accelerated integration in sheep. Although the 3D‐structure of BMP‐2 is known the surface topography has not been the subject of a detailed analysis. Therefore we have begun implementing the technique of 3D‐rapid prototyping as a novel method for gaining topographical information on the structure‐function relationship of proteins (Laub et al., 2001, FASEB J. 15, A543). 3D‐rapid prototyping allows the construction of accurate three‐dimensional models of proteins based on their x‐ray crystallographic data. In this way we constructed a 3D scale image of BMP‐2 of the size 140 mm × 70 mm × 50 mm corresponding to a ca. 20 × 10⁶ fold magnification (scale 1 nm = 2 cm). BMP‐2 is a twisted banana‐shaped molecule consisting of a convex and a concave face and has a horn‐like protuberance cross‐turned at 180° (long axis) at each end. In the center of the convex face there is a ca. 1 nm deep crater like pit ca. 1.8 nm in diameter. The concave face is characterized by a 6–7 nm long helical groove 0.8–1.6 nm wide and ca 0.8 nm deep, into which a left‐handed helix with a pitch of 8–9 nm and a helical radius of 0.35–0.45 nm can be fitted. The concave face of BMP‐2 therefore corresponds to an imprint (groove) of a left‐handed helix i. e. to an anti‐helix or anthelix. The possible endogenous ligands and functions of these structures are unknown. These results demonstrate that full scale 3D molecular models of proteins can lead to new perceptions in understanding the interactions between ligands and proteins by macroscopic viewing and in‐hand fitting of the molecules without the aid of a computer.