Maquinaria de replicação de DNA capturada em detalhes a nível atômico: mero acaso, fortuita necessidade ou design inteligente?

segunda-feira, julho 15, 2019

DNA translocation mechanism of the MCM complex and implications for replication initiation

Martin Meagher, Leslie B. Epling & Eric J. Enemark 

Nature Communications volume 10, Article number: 3117 (2019) 

Fig. 8
Proposed MCM:DNA aspects of replication initiation. 


The DNA translocation activity of the minichromosome maintenance (MCM) complex powers DNA strand separation of the replication forks of eukaryotes and archaea. Here we illustrate an atomic level mechanism for this activity with a crystal structure of an archaeal MCM hexamer bound to single-stranded DNA and nucleotide cofactors. Sequence conservation indicates this rotary mechanism is fully possible for all eukaryotes and archaea. The structure definitively demonstrates the ring orients during translocation with the N-terminal domain leading, indicating that the translocation activity could also provide the physical basis of replication initiation where a double-hexamer idly encircling double-stranded DNA transforms to single-hexamers that encircle only one strand. In this mechanism, each strand binds to the N-terminal tier of one hexamer and the AAA+ tier of the other hexamer such that one ring pulls on the other, aligning equivalent interfaces to enable each hexamer to pull its translocation strand outside of the opposing hexamer.