Nowalk A J, Tencza S B, Mietzner T A
Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pennsylvania 15261.
Biochemistry. 1994 Nov 1;33(43):12769-75. doi: 10.1021/bi00209a007.
The ferric iron-binding protein (Fbp) functions as a periplasmic-binding protein in the high-affinity active transport of growth-essential iron by pathogenic Neisseria. Fbp reversibly binds a single ferric ion per molecule of protein with high affinity. Similarly, the transferrins are a highly conserved family of bilobed vertebrate proteins that reversibly bind a single molecule of iron on each of the N- and C-terminal lobes. While evolutionarily divergent, iron binding by all described transferrin lobes is accomplished by a remarkably similar repertoire of residues, including two Tyr, one His, and one Asp, as well as a synergestic bicarbonate anion. With a molecular mass of ca. 34 kDa, Fbp approximates the size of a transferrin lobe. Given the similarities in iron-binding properties, it was investigated whether Fbp bound iron by a similar molecular strategy as the transferrins. The studies reported here demonstrate that the spectral properties of purified Fbp and human transferrin are similar in the visible range. Chemical modification of purified Fbp in the presence and absence of iron using the Tyr-specific modifier tetranitromethane demonstrates that between two and three Tyr residues are implicated in iron binding. A similar experiment using the His-specific reagent diethyl pyrocarbonate indicates that one of the six Fbp-encoded His residues is protected by iron. In addition, like the transferrins, a bicarbonate anion is required for the efficient coordination of iron by Fbp. The range of metals bound by Fbp and human transferrin, including the luminescent lanthanide terbium, is identical. Finally, terbium derivatives of Fbp and human transferrin yield virtually identical luminescence excitation spectra, implying a highly similar binding site environment. These studies suggest that the prokaryotic Fbp is a mono-sited analog for iron binding by the eukaryotic transferrins.
铁结合蛋白（Fbp）在致病性奈瑟菌对生长必需铁的高亲和力主动转运过程中作为周质结合蛋白发挥作用。Fbp每分子蛋白质可逆地结合单个铁离子，且亲和力高。同样，转铁蛋白是双叶脊椎动物蛋白的一个高度保守家族，在其N端和C端叶上各可逆地结合单个铁分子。虽然在进化上有差异，但所有已描述的转铁蛋白叶的铁结合是通过一组非常相似的残基完成的，包括两个酪氨酸、一个组氨酸和一个天冬氨酸，以及一个协同作用的碳酸氢根阴离子。Fbp分子量约为34 kDa，接近转铁蛋白叶的大小。鉴于铁结合特性的相似性，研究了Fbp是否通过与转铁蛋白相似的分子策略结合铁。此处报道的研究表明，纯化的Fbp和人转铁蛋白在可见光范围内的光谱特性相似。使用酪氨酸特异性修饰剂四硝基甲烷在有铁和无铁的情况下对纯化的Fbp进行化学修饰表明，两到三个酪氨酸残基参与铁结合。使用组氨酸特异性试剂焦碳酸二乙酯进行的类似实验表明，Fbp编码的六个组氨酸残基中的一个受铁保护。此外，与转铁蛋白一样，Fbp有效配位铁需要碳酸氢根阴离子。Fbp和人转铁蛋白结合的金属范围相同，包括发光镧系元素铽。最后，Fbp和人转铁蛋白的铽衍生物产生几乎相同的发光激发光谱，这意味着结合位点环境高度相似。这些研究表明，原核生物的Fbp是真核生物转铁蛋白铁结合的单位点类似物。
