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

Figure 3

Subdomain B contains a zinc-binding motif. (a) All MCM_N X-ray crystal structures contain a zinc atom bound with a tetrahedral geometry. Each structure is depicted in a cartoon representation with zinc-binding side-chains shown in stick. Cysteine sulfurs are colored in yellow, and histidine nitrogen atoms are colored in blue. The remainder of each protein is shown as red, blue, and green for (PDB: 1LTL), (PDB: 4POG), and (PDB: 2VL6), respectively. Zinc atoms are shown as gray spheres. All structure representations of Figure 3 were prepared with the Pymol software package [88]. (b) A multiple sequence alignment shows the strong sequence conservation of the MCM zinc-binding domain. The spacing of the cysteine residues in MCM Zn-binding sequence motifs shows family-specific patterns, where residues displaying a high degree of sequence conservation across all MCM proteins or family-specific sequence conservation have been colored as either green or orange, respectively. Residues involved in zinc-binding are highlighted in blue with a blue dot for emphasis. Mcm3 does not possess an obvious zinc-binding motif, and Mcm5 has an abnormally large spacing between the third and fourth cysteine residues.

(a)

(b)