Histidine tracts in human transcription factors: insight into metal ion coordination ability.

Consecutive histidine repeats are chosen both by nature and by molecular biologists due to their high affinity towards metal ions. Screening of the human genome showed that transcription factors are extremely rich in His tracts. In this work, we examine two of such His-rich regions from forkhead box and MAFA proteins-MB3 (contains 18 His) and MB6 (with 21 His residues), focusing on the affinity and binding modes of Cu and Zn towards the two His-rich regions. In the case of Zn species, the availability of imidazole nitrogen donors enhances metal complex stability. Interestingly, an opposite tendency is observed for Cu complexes at above physiological pH, in which amide nitrogens participate in binding. [ABSTRACT FROM AUTHOR]