Abstract:

The Arg-Gly-Asp sequence(RGD), a ubiquitous adhesive motif in extracellular matrix proteins, exhibits a high affinity to the predominant osteoblast integrin;thus it has been regarded as a promising candidate for biomimic coating to emulate biology in the fabrication of bone-anchored implant surfaces, especially the widely used titanium-based materials.The present study aims to explore the molecular scale events that occur when RGD is placed close to the rutile TiO₂(110) surface by employing classical all-atom molecular dynamics simulations.Local grooves with different depths were introduced in the substrate surfaces to figure out the effect of surface topography on the binding modes of RGD with rutile.The simulation results show that the negatively charged carboxyl groups of RGD are able to break through the barriers from surface hydrations, forming direct bonds with the surface Ti atoms.However, this occurs on the premise that an anchoring site on the rutile surface has been provided to the peptide with an external intervention.Since the unsaturated atoms on the top-layer of groove walls seem to be underlying active sites for peptide adsorption, the presence of surface grooves will largely affect the RGD-rutile binding modes.If RGD can be locked on the bottom of groove via the direct bonds between carboxyl groups and surface Ti atoms, the positively charged groups(guanidine or amino group) are inclined to form hydrogen bonds with surface O atoms on the groove walls, when the length of the rest chain allows.However, once RGD is connected to the bottom of groove with both Arg and Asp side chains “trapped” in a “horseshoe” configuration, the formation of hydrogen bonds between the peptide and the groove walls will be greatly suppressed.The results also indicate that the dominant factors determining the binding strength of RGD-rutile complex are the concrete types of interaction and the number of jointing points.It is anticipated that the findings presented here will ultimately contribute to the biomimetic modification of implants, by suggesting how to tailor the surface topography of implants to induce the desirable biological function.

Key words: rutile, surface topography, peptide, molecular simulation, aqueous solution

摘要：

精氨酸-甘氨酸-天冬氨酸（Arg-Gly-Asp，RGD）序列是细胞膜整合素受体与细胞外配体相结合的识别位点，利用其对材料表面进行仿生修饰可以提高植入体的生物相容性。采用全原子分子动力学方法，模拟研究了RGD与理想和具有不同深度凹槽结构的金红石型TiO₂（110）表面的结合模式和结合稳定性。研究结果表明，在纯水环境下，RGD在金红石表面存在锚定点是该序列中带负电的羧基基团与表面Ti原子直接键合的前提。凹槽侧壁表层的不饱和原子是RGD形成吸附的潜在作用点，故在金红石表面引入凹槽结构能在一定程度上影响该序列同基底之间的结合模式。当RGD通过羧基基团与槽底原子稳定键合之后，若剩余部分的长度足以触及至槽壁区域，则肽链中带正电的氨基或胍基基团与槽壁原子形成氢键的概率较大；若RGD通过两侧末端基团分别同槽底形成了稳定作用，则会显著抑制该序列与槽壁原子之间氢键的形成。RGD序列同金红石表面结合作用的强弱取决于结合点的数量以及相互作用的具体类型。

关键词: 金红石, 表面拓扑结构, 肽, 分子模拟, 水溶液