Elangovan Satheesh, Margolis Henry C, Oppenheim Frank G, Beniash Elia
Department of Periodontology and Oral Biology, Boston University Goldman School of Dental Medicine, Suite W201, 700 Albany Street, Boston, Massachusetts 02118-2392, USA.
Langmuir. 2007 Oct 23;23(22):11200-5. doi: 10.1021/la7013978. Epub 2007 Sep 20.
Conformational analyses of PRP1, a proline-rich acidic salivary protein and major component of the acquired enamel pellicle, have been carried out in solution and upon binding to two enamel prototypes, hydroxyapatite (HA) and carbonated hydroxyapatite (CHA), using Fourier transform infrared spectroscopy (FTIR) in attenuated total reflection (ATR) mode. We have shown for the first time that, in solution, large portions of PRP1 adopt the hydrated polyproline type II (PPII) helical structure in addition to the random coil structure, with the maximum absorbance of the amide I band around 1620 cm(-1). Upon binding to HA or CHA, the protein undergoes significant conformational changes, loosing a considerable portion of hydrated PPII and random coil domains with a shift in the maximum absorbance to 1666 cm(-1), indicating that a large fraction of the protein is composed of beta turns. A small fraction of PPII in a calcium-bound or anhydrous form (approximately 1642 cm(-1)) was also observed in the HA- and CHA-bound proteins, which could play a role in protein-mineral interactions. The conformational changes in PRP1 adsorbed on CHA and HA were similar in nature; however, these changes were greater in the protein bound to HA. Interestingly, these results are in agreement with protein adsorption data that show that less protein is adsorbed onto CHA than onto HA. Our results demonstrate that binding to apatitic mineral surfaces leads to major conformational changes in PRP1, which might reflect the expulsion of water and the formation of protein-mineral and/or protein-protein interactions in the adsorbed layer.
富含脯氨酸的酸性唾液蛋白PRP1是获得性釉质 pellicle的主要成分，已在溶液中以及与两种釉质原型（羟基磷灰石（HA）和碳酸羟基磷灰石（CHA））结合时进行了构象分析，采用衰减全反射（ATR）模式的傅里叶变换红外光谱（FTIR）。我们首次表明，在溶液中，除了无规卷曲结构外，PRP1的大部分还采用水合聚脯氨酸II型（PPII）螺旋结构，酰胺I带的最大吸收峰在1620 cm(-1)左右。与HA或CHA结合后，蛋白质发生显著的构象变化，失去相当一部分水合PPII和无规卷曲结构域，最大吸收峰移至1666 cm(-1)，表明大部分蛋白质由β转角组成。在与HA和CHA结合的蛋白质中也观察到一小部分以钙结合或无水形式存在的PPII（约1642 cm(-1)），这可能在蛋白质-矿物质相互作用中发挥作用。吸附在CHA和HA上的PRP1的构象变化本质上相似；然而，与HA结合的蛋白质中的这些变化更大。有趣的是，这些结果与蛋白质吸附数据一致，该数据表明吸附在CHA上的蛋白质比吸附在HA上的少。我们的结果表明，与磷灰石矿物表面结合会导致PRP1发生主要的构象变化，这可能反映了水的排出以及吸附层中蛋白质-矿物质和/或蛋白质-蛋白质相互作用的形成。
