Dynamics of the Mrf-2 DNA-binding domain free and in complex with DNA.

Mrf-2 is a member of a new class of DNA-binding proteins known as the AT-rich interaction domain family or ARID. Chemical shift indices and characteristic NOE values indicate that the three-dimensional structure of the Mrf-2 ARID in complex with DNA is nearly identical to that of the free protein. The backbone dynamics of the Mrf-2 domain free and in complex with DNA have been characterized by (15)N NMR relaxation measurements and model-free analysis. Chemical shift perturbations and dynamic studies suggest that two flexible interhelical loops, the flexible C-terminal tail, and one alpha-helix are involved in DNA recognition, indicating the importance of protein dynamics in DNA binding. Some well-structured regions, in particular the putative DNA-contacting helix, in Mrf-2 show a decrease in the order parameters (S(2)) upon complex formation. The less well-structured loops and the unstructured C-terminus show reduced flexibility upon DNA binding. In addition, the model-free analysis indicates motions on the picosecond to nanosecond and micro- to millisecond time scales at the DNA-binding surface of the bound Mrf-2 ARID, suggesting a model where interactions between the protein and DNA are highly dynamic.