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首页> 美国卫生研究院文献>Frontiers in Physiology >The expanded amelogenin polyproline region preferentially binds to apatite versus carbonate and promotes apatite crystal elongation
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The expanded amelogenin polyproline region preferentially binds to apatite versus carbonate and promotes apatite crystal elongation

机译：扩大的釉原蛋白多脯氨酸区域优先结合磷灰石而不是碳酸盐并促进磷灰石晶体伸长

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The transition from invertebrate calcium carbonate-based calcite and aragonite exo- and endoskeletons to the calcium phosphate-based vertebrate backbones and jaws composed of microscopic hydroxyapatite crystals is one of the great revolutions in the evolution of terrestrial organisms. To identify potential factors that might have played a role in such a transition, three key domains of the vertebrate tooth enamel protein amelogenin were probed for calcium mineral/protein interactions and their ability to promote calcium phosphate and calcium carbonate crystal growth. Under calcium phosphate crystal growth conditions, only the carboxy-terminus augmented polyproline repeat peptide, but not the N-terminal peptide nor the polyproline repeat peptide alone, promoted the formation of thin and parallel crystallites resembling those of bone and initial enamel. In contrast, under calcium carbonate crystal growth conditions, all three amelogenin-derived polypeptides caused calcium carbonate to form fused crystalline conglomerates. When examined for long-term crystal growth, polyproline repeat peptides of increasing length promoted the growth of shorter calcium carbonate crystals with broader basis, contrary to the positive correlation between polyproline repeat element length and apatite mineralization published earlier. To determine whether the positive correlation between polyproline repeat element length and apatite crystal growth versus the inverse correlation between polyproline repeat length and calcium carbonate crystal growth were related to the binding affinity of the polyproline domain to either apatite or carbonate, a parallel series of calcium carbonate and calcium phosphate/apatite protein binding studies was conducted. These studies demonstrated a remarkable binding affinity between the augmented amelogenin polyproline repeat region and calcium phosphates, and almost no binding to calcium carbonates. In contrast, the amelogenin N-terminus bound to both carbonate and apatite, but preferentially to calcium carbonate. Together, these studies highlight the specific binding affinity of the augmented amelogenin polyproline repeat region to calcium phosphates versus calcium carbonate, and its unique role in the growth of thin apatite crystals as they occur in vertebrate biominerals. Our data suggest that the rise of apatite-based biominerals in vertebrates might have been facilitated by a rapid evolution of specialized polyproline repeat proteins flanked by a charged domain, resulting in apatite crystals with reduced width, increased length, and tailored biomechanical properties.
机译：从无脊椎动物的碳酸钙方解石和文石的外骨架和内骨架到由微观的羟基磷灰石晶体组成的磷酸钙基的脊椎动物骨干和颚骨的过渡是陆地生物进化的重大革命之一。为了确定可能在这种过渡过程中起作用的潜在因素，对脊椎动物牙釉质蛋白牙釉蛋白的三个关键域进行了钙矿物质/蛋白质相互作用及其促进磷酸钙和碳酸钙晶体生长的能力的探测。在磷酸钙晶体生长条件下，仅羧基末端增强的聚脯氨酸重复肽，而不是单独的N末端肽或聚脯氨酸重复肽，促进了类似于骨骼和初始釉质的薄而平行的微晶的形成。相反，在碳酸钙晶体生长条件下，所有三种釉素衍生多肽均导致碳酸钙形成融合的结晶团块。当检查晶体的长期生长时，长度增加的聚脯氨酸重复肽促进了更短的碳酸钙晶体的生长，具有更广阔的基础，这与聚脯氨酸重复元素长度与磷灰石矿化之间的正相关性相反。为了确定聚脯氨酸重复元件长度与磷灰石晶体生长之间的正相关与聚脯氨酸重复序列长度与碳酸钙晶体生长之间的负相关是否与聚脯氨酸域与磷灰石或碳酸钙（碳酸钙平行系列）的结合亲和力相关并进行了磷酸钙/磷灰石蛋白结合研究。这些研究表明增强的釉原蛋白多脯氨酸重复区域与磷酸钙之间具有显着的结合亲和力，并且几乎不与碳酸钙结合。相反，牙釉蛋白N-末端与碳酸盐和磷灰石都结合，但优先与碳酸钙结合。总之，这些研究突出了增强的釉原蛋白多脯氨酸重复序列区域对磷酸钙与碳酸钙的特异性结合亲和力，以及其在脊椎动物生物矿物中出现的磷灰石薄晶体生长中的独特作用。我们的数据表明，脊椎动物中基于磷灰石的生物矿物质的增加可能是由沿带电域侧翼的特殊聚脯氨酸重复蛋白的快速进化所促进的，从而导致磷灰石晶体的宽度减小，长度增加，并且具有定制的生物力学特性。

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