Grossoehme Nicholas E, Akilesh Shreeram, Guerinot Mary Lou, Wilcox Dean E
Departments of Chemistry and Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA.
Inorg Chem. 2006 Oct 16;45(21):8500-8. doi: 10.1021/ic0606431.
The widespread ZIP family of transmembrane metal-transporting proteins is characterized by a large intracellular loop that contains a histidine-rich sequence whose biological role is unknown. To provide a chemical basis for this role, we prepared and studied a peptide corresponding to this sequence from the first iron-regulated transporter (IRT1) of Arabidopsis thaliana, which transports Fe2+ as well as Mn2+, Co2+, Zn2+, and Cd2+. Isothermal titration calorimetry (ITC) measurements, which required novel experiments and data analysis, and supporting spectroscopic methods were used to quantify IRT1's metal-binding affinity and associated thermodynamics. The peptide, PHGHGHGHGP, binds metal ions with 1:1 stoichiometry and stabilities that are consistent with the Irving-Williams series. Comparison of the metal-binding thermodynamics of the peptide with those of trien provides new insight about enthalpic and entropic contributions to the stability of the metal-peptide complex. Although Fe2+ and other IRT1-transported metal ions do not bind very tightly, this His-rich sequence has a very high entropy-driven affinity for Fe3+, which may have biological significance.
广泛存在的ZIP跨膜金属转运蛋白家族的特征是具有一个大的细胞内环，该环包含一个富含组氨酸的序列，其生物学作用尚不清楚。为了为该作用提供化学基础，我们制备并研究了一种与拟南芥首个铁调节转运蛋白（IRT1）的该序列相对应的肽，IRT1可转运Fe2+以及Mn2+、Co2+、Zn2+和Cd2+。等温滴定量热法（ITC）测量需要新颖的实验和数据分析，并使用支持性光谱方法来量化IRT1的金属结合亲和力及相关热力学。该肽PHGHGHGHGP以1:1的化学计量比结合金属离子，其稳定性与欧文-威廉姆斯序列一致。将该肽的金属结合热力学与三亚乙基四胺的进行比较，为焓和熵对金属-肽复合物稳定性的贡献提供了新的见解。尽管Fe2+和其他IRT1转运的金属离子结合不太紧密，但这个富含组氨酸的序列对Fe3+具有非常高的熵驱动亲和力，这可能具有生物学意义。
