Structural studies of the archaeal MCM complex in different functional states.
The primary candidate for the eukaryotic replicative helicase is the MCM2-7 complex, a hetero-oligomer formed by six AAA+ paralogous polypeptides. A simplified model for structure-function studies is the homo-oligomeric orthologue from the archaeon Methanothermobacter thermoautotrophicus. The crystal structure of the DNA-interacting N-terminal domain of this homo-oligomer revealed a double hexamer in a head-to-head configuration; single-particle electron microscopy studies have shown that the full-length protein complex can form both single and double rings, in which each ring can consist of a cyclical arrangement of six or seven subunits. Using single-particle techniques and especially multivariate statistical symmetry analysis, we have assessed the changes in stoichiometry that the complex undergoes when treated with various nucleotide analogues or when binding a double-stranded DNA fragment. We found that the binding of nucleotides or of double-stranded DNA leads to the preferred formation of double-ring structures. Specifically, the protein complex is present as a double heptamer when treated with a nucleotide analogue, but it is rather found as a double hexamer when complexed with double-stranded DNA. The possible physiological role of the various stoichiometries of the complex is discussed in the light of the proposed mechanisms of helicase activity.
Costa
Alessandro
A
Division of Cell and Molecular Biology, Imperial College London SW7 2AZ, UK.
Pape
Tillmann
T
van Heel
Marin
M
Brick
Peter
P
Patwardhan
Ardan
A
Onesti
Silvia
S
D000244:Adenosine Diphosphate / Q000494:pharmacology; D019843:Archaeal Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism* / Q000648:ultrastructure; D019847:Chromosomes, Archaeal / Q000737:chemistry / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D004265:DNA Helicases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D017013:Methanobacteriaceae / Q000201:enzymology; D008954:Models, Biological; D009711:Nucleotides / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity; D014170:Transformation, Genetic
D019843:Archaeal Proteins; D009711:Nucleotides; D000244:Adenosine Diphosphate; D004247:DNA; D004265:DNA Helicases