Olfactomedins are a family of modular proteins found in multicellular organisms that all contain five-bladed β-propeller olfactomedin (OLF) domains. In support of differential functions for the OLF propeller, the available crystal structures reveal that only some OLF domains harbor an internal calcium-binding site with ligands derived from a triad of residues. For the myocilin OLF domain (myoc-OLF), ablation of the ion-binding site (triad Asp, Asn, Asp) by altering the coordinating residues affects the stability and overall structure, in one case leading to misfolding and glaucoma. Bioinformatics analysis reveals a variety of triads with possible ion-binding characteristics lurking in OLF domains in invertebrate chordates such as Arthropoda (Asp-Glu-Ser), Nematoda (Asp-Asp-His) and Echinodermata (Asp-Glu-Lys). To test ion binding and to extend the observed connection between ion binding and distal structural rearrangements, consensus triads from these phyla were installed in the myoc-OLF. All three protein variants exhibit wild-type-like or better stability, but their calcium-binding properties differ, concomitant with new structural deviations from wild-type myoc-OLF. Taken together, the results indicate that calcium binding is not intrinsically destabilizing to myoc-OLF or required to observe a well ordered side helix, and that ion binding is a differential feature that may underlie the largely elusive biological function of OLF propellers.

中文翻译：

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从无脊椎动物门中选择的 myocilin olfactomedin 螺旋桨的钙配体变体揭示了与 N 端叶片和表面螺旋的串扰。

Olfactomedin 是在多细胞生物体中发现的一个模块化蛋白家族，全部含有五叶 β-螺旋桨 olfactomedin (OLF) 结构域。为了支持 OLF 螺旋桨的差异功能，可用的晶体结构表明，只有一些 OLF 结构域具有内部钙结合位点，其配体源自三联体残基。对于肌纤蛋白 OLF 结构域 (myoc-OLF)，通过改变配位残基来消除离子结合位点（三联体 Asp、Asn、Asp）会影响稳定性和整体结构，在一种情况下会导致错误折叠和青光眼。生物信息学分析揭示了无脊椎动物脊索动物 OLF 结构域中潜伏着多种可能具有离子结合特征的三联体，例如节肢动物 (Asp-Glu-Ser)、线虫动物 (Asp-Asp-His) 和棘皮动物 (Asp-Glu-Lys)。为了测试离子结合并扩展离子结合和远端结构重排之间观察到的联系，将来自这些门的共有三联体安装在 myoc-OLF 中。所有三种蛋白质变体都表现出与野生型类似或更好的稳定性，但它们的钙结合特性不同，伴随着与野生型 myoc-OLF 的新结构偏差。综上所述，结果表明，钙结合本质上不会破坏 myoc-OLF 的稳定性，也不是观察有序侧螺旋所必需的，而且离子结合是一种差异特征，可能是 OLF 螺旋桨难以捉摸的生物学功能的基础。