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

Figure 4

Crystal structure of a nearly full length MCM hexamer. An ADP-bound, nearly full length MCM protein was crystallized by creating a chimeric fusion protein of the N-terminal domain of SsoMCM and the C-terminal tier of PfMCM. (a) Views of the Sso-PfMCM hexamer crystal structure parallel and perpendicular to the central channel with each subunit uniquely colored. Magnesium ions are shown as magenta spheres, ADP molecules are shown in space-filling view, and zinc ions are shown as gray spheres. In the view parallel to the central channel, the ATPase domains are projected out of the page. In the perpendicular view, the ATPase domains are located at the top and the N-terminal domains are located on the bottom. (b) The ATPase site is formed at subunit interfaces by cis- and trans-acting residues shown in stick and labeled. The Walker A and Walker B residues of one subunit are positioned at the left side of the site (yellow), while three basic residues are located on the right side of the site (blue). The bound ADP molecule is shown in stick, and the magnesium ion is represented as a magenta sphere. (c) Residues of the allosteric communication loop (ACL) interact across subunit interfaces and also with main-chain atoms of the helix-2-insert (h2i) β-hairpin motif. The ACL is shown in blue and the h2i and presensor-1-β-hairpin (ps1β) are shown in yellow and orange, respectively. Dashed lines indicate the discussed molecular interactions. All structure representations of Figure 4 were prepared with the Pymol software package [88] and PDB accession code 4R7Y.

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