Fig. 1: Subunit rotation model of serine recombinase-catalysed site-specific recombination.
From: Direct observation of subunit rotation during DNA strand exchange by serine recombinases
A 1. The synaptic complex contains a serine recombinase tetramer (purple and blue ovals) bridging two double-stranded recognition sites (black and yellow lines). The catalytic serine residue is shown as S-OH, and the scissile phosphodiesters are labelled P. Donor and acceptor fluorophores at DNA attachment points that allow the mechanism to be tracked by changes in FRET efficiency are represented as green and red stars. 2. Nucleophilic attack by the hydroxyl groups of the serine residues cleaves the double-stranded DNA with a 2-bp stagger, leaving ends with a 5’-phosphoserine linkage and a 3′-OH. 3. For strand exchange, one complete half of the complex is rotated by 180° using the flat hydrophobic interface as a rotational bearing. 4. Subsequent ligation of the strands takes place by attack on the 5′-phosphoseryl linkages by the deoxyribose 3′-OH ends. B Co-crystal structure of a wild-type γδ resolvase dimer bound to site I DNA. (PDBid 1gdt7) C. Activated γδ resolvase mutant tetramer bound to two site Is in the post-cleavage covalent protein-DNA synaptic intermediate state (PDBid 1zr49).
