The solution structure of full‐length dodecameric MCM by SANS and molecular modeling

The solution structure of the full‐length DNA helicase minichromosome maintenance protein from Methanothermobacter thermautotrophicus was determined by small‐angle neutron scattering (SANS) data together with all‐atom molecular modeling. The data were fit best with a dodecamer (dimer of hexamers). The 12 monomers were linked together by the B/C domains, and the adenosine triphosphatase (AAA+) catalytic regions were found to be freely movable in the full‐length dodecamer both in the presence and absence of Mg²⁺ and 50‐meric single‐stranded DNA (ssDNA). In particular, the SANS data and molecular modeling indicate that all 12 AAA+ domains in the dodecamer lie approximately the same distance from the axis of the molecule, but the positions of the helix–turn–helix region at the C‐terminus of each monomer differ. In addition, the A domain at the N‐terminus of each monomer is tucked up next to the AAA+ domain for all 12 monomers of the dodecamer. Finally, binding of ssDNA does not lock the AAA+ domains in any specific position, which leaves them with the flexibility to move both for helicase function and for binding along the ssDNA. Proteins 2014; 82:2364–2374. © 2014 Wiley Periodicals, Inc.