Archaeal MCM Proteins as an Analog for the Eukaryotic Mcm2–7 Helicase to Reveal Essential Features of Structure and Function

Figure 7

Comparison of MCM with representative members of other hexameric helicase superfamilies. The hexameric MCM structure viewed either perpendicular (a) or parallel (b) to the central channel axis. The MCM h2i and ps1β central channel modules are colored yellow and orange, respectively. (c–h) Comparison with representative members of other helicase superfamilies such as E1 ((c-d), SFIII, PDB: 2XGA), DnaB ((e-f), SFIV, PDB: 4ESV), and Rho ((g-h), SFV, PDB: 3ICE) suggests that MCM central channel modules will move “up” and “down” to translocate DNA. In the crystal structures of each of these hexameric helicases, basic residues on loops projected into the central channel interact with nucleic acid in a spiral-staircase-like arrangement. In this mode of binding, the central channel loops from adjacent subunits occupy different heights around the ring to form a “spiral-staircase” shape. The movement of DNA is then achieved by the movement of the central channel loops. DNA is colored in teal and DNA binding loops are colored orange. All structures are viewed either perpendicular (left column) or parallel (right column) to the central channel axis. All structure representations of Figure 7 were prepared with the Pymol software package [88].