Department of Chemistry & Biochemistry, The University of Alabama, 250 Hackberry Lane, Tuscaloosa, AL 35487-0336, USA.
Center for Advanced Microstructure & Devices, Louisiana State University, 6980 Jefferson Highway, Baton Rouge, LA 70806, USA.
J Inorg Biochem. 2020 Sep;210:111101. doi: 10.1016/j.jinorgbio.2020.111101. Epub 2020 May 23.
Transferrin, the Fe(III) transport protein in mammalian blood, has been suggested to also serve as a Cr(III) transporter and as part of a Cr(III) detoxification system; however, the structure of the metal-binding sites has never been fully elucidated with bound Cr(III). Chromium(III)-transferrin was crystallized in the presence of the synergistic anion malonate. In the crystals, the protein exists with a closed C-terminal lobe containing a Cr(III) ion and an open, unoccupied N-terminal lobe. The overall structure and the metal ion environments are extremely similar to those of Fe(III)- and Ti(IV)-containing transferrin crystallized under comparable conditions. The octahedral coordination about the Cr(III) is comprised of four ligands provided by the protein (two tyrosine residues, a histidine residue, and an aspartate residue) and a chelating malonate anion. This represents the first crystal structure of a Cr(III)-containing protein that binds Cr(III) as part of its physiological function.
转铁蛋白是哺乳动物血液中 Fe(III)的转运蛋白，据推测它也可以作为 Cr(III)的转运蛋白，并作为 Cr(III)解毒系统的一部分；然而，与结合的 Cr(III)一起，其金属结合位点的结构从未被完全阐明。在协同阴离子丙二酸的存在下，对铬（III）-转铁蛋白进行了结晶。在晶体中，该蛋白质存在于含有 Cr(III)离子的封闭 C 端叶和开放、未占据的 N 端叶中。整体结构和金属离子环境与在类似条件下结晶的含 Fe(III)和 Ti(IV)的转铁蛋白非常相似。Cr(III)的八面体配位由蛋白质提供的四个配体组成（两个酪氨酸残基、一个组氨酸残基和一个天冬氨酸残基）和一个螯合丙二酸阴离子。这代表了第一个结合 Cr(III)作为其生理功能一部分的 Cr(III)结合蛋白的晶体结构。
