Moradian-Oldak Janet, Bouropoulos Nikolaos, Wang Lingli, Gharakhanian Narbeh
Center for Craniofacial Molecular Biology, School of Dentistry, University of Southern California, 2250 Alcazar Street, Los Angeles, CA 90033, USA.
Matrix Biol. 2002 Mar;21(2):197-205. doi: 10.1016/s0945-053x(01)00190-1.
Amelogenins, the major protein component of the mineralizing enamel extracellular matrix, are critical for normal enamel formation as documented in the linkage studies of a group of inherited disorders, with defective enamel formation, called Amelogenesis imperfecta. Recent cases of Amelogenesis imperfecta include mutations that resulted in truncated amelogenin protein lacking the hydrophilic C-terminal amino acids. Current advances in knowledge on amelogenin structure, nanospheres assembly and their effects on crystal growth have supported the hypothesis that amelogenin nanospheres provide the organized microstructure for the initiation and modulated growth of enamel apatite crystals. In order to evaluate the function of the conserved hydrophilic C-terminal telopeptide during enamel biomineralization, the present study was designed to analyze the self-assembly and apatite binding behavior of amelogenin proteins and their isoforms lacking the hydrophilic C-terminal. We applied dynamic light scattering to investigate the size distribution of amelogenin nanospheres formed by a series of native and recombinant proteins. In addition, the apatite binding properties of these amelogenins were examined using commercially available hydroxyapatite crystals. Amelogenins lacking the carboxy-terminal (native P161 and recombinant rM166) formed larger nanospheres than those formed by their full-length precursors: native P173 and recombinant rM179. These data suggest that after removal of the hydrophilic carboxy-terminal segment further association of the nanospheres takes place through hydrophobic interactions. The affinity of amelogenins lacking the carboxy-terminal regions to apatite crystals was significantly lower than their parent amelogenins. These structure-functional analyses suggest that the hydrophilic carboxy-terminal plays critical functional roles in mineralization of enamel and that the lack of this segment causes abnormal mineralization.
釉原蛋白是矿化釉质细胞外基质的主要蛋白质成分，对于正常釉质形成至关重要，这在一组遗传性疾病的连锁研究中得到了证实，这些疾病的釉质形成存在缺陷，称为釉质发育不全。最近的釉质发育不全病例包括导致截短的釉原蛋白缺乏亲水性C末端氨基酸的突变。目前关于釉原蛋白结构、纳米球组装及其对晶体生长影响的知识进展支持了这样一种假说，即釉原蛋白纳米球为釉质磷灰石晶体的起始和调节生长提供了有组织的微观结构。为了评估保守的亲水性C末端肽段在釉质生物矿化过程中的功能，本研究旨在分析釉原蛋白及其缺乏亲水性C末端的异构体的自组装和磷灰石结合行为。我们应用动态光散射来研究由一系列天然和重组蛋白形成的釉原蛋白纳米球的大小分布。此外，使用市售的羟基磷灰石晶体检测了这些釉原蛋白的磷灰石结合特性。缺乏羧基末端的釉原蛋白（天然P161和重组rM166）形成的纳米球比其全长前体：天然P173和重组rM179形成的纳米球更大。这些数据表明，去除亲水性羧基末端片段后，纳米球通过疏水相互作用进一步缔合。缺乏羧基末端区域的釉原蛋白对磷灰石晶体的亲和力明显低于其亲本釉原蛋白。这些结构-功能分析表明，亲水性羧基末端在釉质矿化中起关键功能作用，缺乏该片段会导致矿化异常。
