 | Acta Crystallographica Section F Acta Crystallographica Section F STRUCTURAL BIOLOGY COMMUNICATIONS |
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![[Figure 4]](ek5022fig4mag.jpg)
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Figure 4
An extended interface can stabilize MCM open rings for loading. (a) An open-ring hexamer model was generated by superimposing the SsoMCM-N dimer in the current study (orange and red subunits) onto the closed-ring SsoMCM-N hexamer (PDB entry 2vl6; Liu et al., 2008  ) based on OB-fold residues 109–132 of chain A. Chains A and B of PDB entry 2vl6 were removed for a clearer view of the open-ring models. The resulting model has an open interface between the red and purple subunits, clockwise to the extended interface. The highly symmetric closed-ring structure of PDB entry 2vl6 (Liu et al., 2008) is illustrated on the right. The structures and orientations of the OB-fold β-barrels are emphasized by a cyan tube with a magenta stripe. The angle between the β-barrels is more obtuse in the extended interface than in the closed-ring interfaces. (b) Similarly, the MCM open ring in eukaryotic OOCM (PDB entry 5v8f; Zhai et al., 2017) has an extended interface between Mcm3 (orange) and Mcm5 (red) that correlates with an open clockwise interface between Mcm5 and Mcm2 (purple), similar to the open-ring model of Fig. 4(a). The structures and orientations of the OB-fold β-barrels are emphasized with a cyan tube with a magenta stripe as in (a). The Mcm2-7 N-terminal tier is illustrated in opaque view in front of the C-terminal tier in transparent view. The Orc1-6 and Cdc6 subunits are beneath the Mcm2-7 C-terminal tier and are excluded for clarity. Cdt1 is shown in a transparent view. Notably, the Mcm2-7 N-terminal tier does not simply track the C-terminal tier during ring closure because the tiers move in opposite directions (see Supplementary Video S1). |
![[Figure 4]](ek5022fig4.jpg)
| STRUCTURAL BIOLOGY COMMUNICATIONS |
ISSN: 2053-230X
