Molecular structure of human topoisomerase II alpha revealed by atomic force microscopy.

The entire human topoisomerase II alpha (hTopoII alpha) dimer was expressed in the yeast Saccaromyces cerevisiae, purified to homogeneity, and subjected to atomic force microscopy (AFM) under a tapping mode. Molecular images obtained exhibited a 'heart or donut-like' structure with a large axial hole. The main benefit of the application of AFM to study the hTopoII alpha is that clear images of the internal 'pore' have been achieved without crystallization, staining, or fixation of the sample. These images are consistent with the model in which topoisomerase II has a large internal gate for DNA strand passage.