Jacob Blackmon B, Dailey Tamara A, Lianchun Xiao, Dailey Harry A
Biomedical and Health Sciences Institute, Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602-7229, USA.
Arch Biochem Biophys. 2002 Nov 15;407(2):196-201. doi: 10.1016/s0003-9861(02)00471-x.
The cDNA for p22HBP has been cloned from human and mouse, and the protein expressed, purified, and characterized. Both mouse and human proteins bind heme and porphyrins with micromolar K(d)s, are highly homologous, monomeric, and soluble, and have a cytoplasmic location. The proteins bind metalloporphyrins, free porphyrins, and N-methylprotoporphyrin with similar affinities, and mutations of a selected set of putative metal ligating residues did not have any significant effect on the measured K(d)s. That the presence or absence of metal in the porphyrin has no effect on the binding constants and the observation that the EPR signal for heme does not change upon binding to the protein strongly suggest that p22HBP is a generic tetrapyrrole-binding protein rather than a dedicated heme-binding protein. A role for p22HBP in cellular porphyrin metabolism is discussed.
p22HBP的互补DNA已从人和小鼠中克隆出来，其表达的蛋白质也已得到纯化和表征。小鼠和人类的蛋白质都以微摩尔级的解离常数（K(d)）与血红素和卟啉结合，它们高度同源、呈单体结构且可溶，定位于细胞质中。这些蛋白质以相似的亲和力结合金属卟啉、游离卟啉和N - 甲基原卟啉，对一组选定的假定金属连接残基进行突变，对所测得的解离常数没有任何显著影响。卟啉中金属的存在与否对结合常数没有影响，并且血红素与该蛋白质结合后电子顺磁共振信号不发生变化，这些观察结果有力地表明，p22HBP是一种通用的四吡咯结合蛋白，而不是专门的血红素结合蛋白。文中还讨论了p22HBP在细胞卟啉代谢中的作用。
