Laboratory for Chemical Physics, Division of Basic Sciences and Craniofacial Biology, New York University, 345 E. 24th Street, NY 10010, USA.
Biochemistry. 2013 Aug 20;52(33):5696-703. doi: 10.1021/bi400808j. Epub 2013 Aug 1.
The formation of the nacre pearl in marine invertebrates represents an on-demand production of mineralization in response to an irritant or parasite threat to the mantle organ. In the Japanese pearl oyster (Pinctada fucata), this process is mediated by a 12-member protein family known as PFMG (Pinctada fucata mantle gene). One of these proteins, PFGM1, has been implicated in modulating calcium carbonate crystal growth and has been reported to possess an EF-hand-like domain. In this report, we establish that the recombinant PFMG1 (rPFMG1) is an intrinsically disordered "imitator" EF-hand protein that increases the number of calcium carbonate mineral crystals that form relative to control scenarios and does not induce aragonite formation. This protein possesses a modified pseudo-EF-hand sequence at the C-terminal end which exhibits low homology (30-40%) to the pseudo-EF-hand mitochondrial SCaMCs buffering/solute transport proteins. This low sequence homology is the result of the inclusion of disorder-promoting amino acids and short amyloid-like aggregation-prone cross-β-strand sequences within the putative PFMG1 pseudo-EF-hand sequence region. Similar to other nacre proteins, rPFMG1 oligomerizes to form amorphous, heterogeneously sized protein oligomers and films in vitro, and this process is enhanced by Ca(2+), which promotes the formation of aggregation-prone extended β-strand structure within rPFMG1. From these results, we conclude that PFMG1 forms supramolecular assemblies that play an important role in amplifying the nucleation process that is crucial for coating or neutralizing invasive threats to the mantle organ.
海洋无脊椎动物珍珠层的形成代表了一种按需矿化反应，以应对外套膜器官受到刺激或寄生虫威胁。在日本珍珠贝（Pinctada fucata）中，这一过程是由一个由 12 个成员组成的蛋白质家族介导的，称为 PFMG（Pinctada fucata 外套膜基因）。这些蛋白质之一，PFGM1，被认为可以调节碳酸钙晶体的生长，并被报道具有 EF 手样结构域。在本报告中，我们确定重组 PFMG1（rPFMG1）是一种内在无序的“模拟”EF 手蛋白，与对照情况相比，它增加了碳酸钙矿晶体的形成数量，并且不会诱导霰石形成。该蛋白在 C 末端具有修饰的拟 EF 手序列，与拟 EF 手线粒体 SCaMCs 缓冲/溶质转运蛋白的同源性较低（30-40%）。这种低序列同源性是由于无序促进氨基酸和短的淀粉样聚集倾向的交叉-β-链序列的包含在假定的 PFMG1 拟 EF 手序列区域内。与其他珍珠层蛋白一样，rPFMG1 寡聚化形成无定形、异质大小的蛋白质寡聚体和体外薄膜，并且该过程被 Ca（2+）增强，Ca（2+）促进 rPFMG1 中易于聚集的延伸 β-链结构的形成。根据这些结果，我们得出结论，PFMG1 形成超分子组装体，在外套膜器官受到刺激或寄生虫威胁时，对放大成核过程发挥重要作用，成核过程对涂层或中和入侵威胁至关重要。
