School of Chemistry and Chemical Engineering, Guangdong Provincial Key Lab for Green Chemical Product Technology, South China University of Technology, Guangzhou 510640, P. R. China.
Langmuir. 2021 Mar 23;37(11):3410-3419. doi: 10.1021/acs.langmuir.0c03626. Epub 2021 Mar 10.
Hydroxyapatite (HAP) is one of the most important inorganic components in biological minerals such as bones and teeth. More than 90% of the total citrate is accumulated in human bones and other biomineralized tissues. In addition, mineralizing proteins are enriched in glutamate and aspartate residues, which are important for their mineral-regulating properties. However, how citrate ions (CITs) and/or acidic amino acids regulate the formation of HAP is still unclear. In this work, molecular dynamics simulations were performed to study how CIT regulates the adsorption behavior of polyaspartic acid (PASP) on the HAP surface in the calcium phosphate solution. The simulation results indicate that PASP can be used as an ion chelator to complex Ca and can serve as templates for HAP mineralization by templating the distribution of Ca on its surface, which are attributed to the -COO and α-helix structure. Most importantly, the orientation distributions of PASP in all systems are narrower with the help of CIT, thereby PASP can be adsorbed on the HAP surface stably with a "lying-down" orientation. This indicates that CIT can be used as a bridging agent to bond the acidic peptide to the HAP surface in biomineralization. Thus, the synergic role of CIT and the acidic peptide on the HAP surface were revealed in this work, which can provide new insights into the interfacial phenomena during the biomineralization.
羟基磷灰石（HAP）是骨骼和牙齿等生物矿物质中最重要的无机成分之一。超过 90%的柠檬酸总量积累在人体骨骼和其他生物矿化组织中。此外，矿化蛋白富含谷氨酸和天冬氨酸残基，这对于它们的矿物质调节特性非常重要。然而，柠檬酸离子（CITs）和/或酸性氨基酸如何调节 HAP 的形成仍不清楚。在这项工作中，进行了分子动力学模拟，以研究 CIT 如何调节柠檬酸根离子在磷酸钙溶液中调节聚天冬氨酸（PASP）在 HAP 表面上的吸附行为。模拟结果表明，PASP 可以用作钙的螯合剂，并通过在其表面上模板化 Ca 的分布来充当 HAP 矿化的模板，这归因于-COO 和α-螺旋结构。最重要的是，CIT 的帮助下，所有系统中 PASP 的取向分布变窄，从而 PASP 可以稳定地以“躺下”的取向吸附在 HAP 表面上。这表明 CIT 可以用作桥联剂将酸性肽键合到 HAP 表面上，从而在矿化过程中揭示 CIT 和酸性肽在 HAP 表面上的协同作用，这可为生物矿化过程中的界面现象提供新的见解。
