Lipocalins are a superfamily of functionally diverse proteins defined by a well‐conserved tertiary structure despite variation in sequence. Lipocalins bind and transport small hydrophobic molecules in organisms of all kingdoms. However, there is still uncertainty regarding the function of some members of the family, including bacterial lipocalin Blc from Escherichia coli. Here, we present evidence that lipocalin Blc may be involved in heme binding, trans‐periplasmic transport, or heme storage. This conclusion is supported by a cocrystal structure, mass‐spectrometric data, absorption titration, and in silico analysis. Binding of heme is observed at low micromolar range with one‐to‐one ligand‐to‐protein stoichiometry. However, the absence of classical coordination to the iron atom leaves the possibility that the primary ligand of Blc is another tetrapyrrole.

中文翻译：

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Lipocalin Blc 是一种潜在的血红素结合蛋白

脂质运载蛋白是功能多样的蛋白质超家族，尽管序列发生变化，但由高度保守的三级结构定义。脂质运载蛋白结合并运输所有界生物体中的小疏水分子。然而，该家族某些成员的功能仍存在不确定性，包括来自大肠杆菌的细菌脂质运载蛋白 Blc。在这里，我们提出了 lipocalin Blc 可能参与血红素结合、跨周质转运或血红素储存的证据。这一结论得到了共晶结构、质谱数据、吸收滴定和计算机分析的支持。在低微摩尔范围内观察到血红素的结合，具有一对一的配体与蛋白质的化学计量。然而，