9YI7

Cryo-EM structure of yeast Mgm101 bound to duplex DNA annealing intermediate

Summary for 9YI7

• Entry DOI: 10.2210/pdb9yi7/pdb
• EMDB information: 72980
• Descriptor: ssDNA (75+), ssDNA (75-), Mitochondrial genome maintenance protein MGM101 (3 entities in total)
• Functional Keywords: single strand annealing protein, ssap, annealase, dna binding protein, dna binding protein-dna complex, dna binding protein/dna
• Biological source: Saccharomyces cerevisiae (brewer's yeast); More
• Total number of polymer chains: 21
• Total formula weight: 569430.93

Authors

Wheat, C.T.,Bell, C.E. (deposition date: 2025-10-01, release date: 2025-11-05, Last modification date: 2025-12-10)

Primary citation

Wheat, C.T.,Qi, Z.,Hussain, M.,Zakharova, K.,Wysocki, V.H.,Bell, C.E.
Mechanism of single-strand annealing from native mass spectrometry and cryo-EM structures of RAD52 homolog Mgm101.
Biorxiv, 2025

PubMed Abstract: RAD52, the primary single-strand annealing (SSA) protein in humans, forms undecameric rings that bind ssDNA within a narrow, positively-charged groove. Whether RAD52 anneals two complementary ssDNAs on the same ring in , or between two ring-ssDNA complexes in , is unknown. Here, we determined cryo-EM structures of Mgm101, a RAD52 homolog from yeast mitochondria, in complexes with ssDNA, a duplex intermediate of annealing, and B-form dsDNA product. In all states, Mgm101 forms a closed nonadecameric ring that binds the backbone of the first ssDNA at the base of the narrow groove. The second complementary strand binds directly on top of the first to form an extended, unwound, and circular duplex intermediate of annealing. The third complex captures apparent B-form DNA product bound to a novel β-hairpin motif located on top of the Mgm101 ring, above the primary DNA-binding groove. Mass photometry and native mass spectrometry confirm and further elucidate the complexes formed in solution. Altogether, our data reveal the full SSA pathway of Mgm101 and suggest it anneals two complementary ssDNAs on the same ring in . Structural conservation with RAD52 suggests it is likely to use a similar mechanism of annealing.

PubMed: 41280126
DOI: 10.1101/2025.10.26.684629

Experimental method

ELECTRON MICROSCOPY (2.54 Å)