Human MutLγ, the MLH1–MLH3 heterodimer, is an endonuclease that promotes DNA expansion

MutL proteins are ubiquitous and play important roles in DNA metabolism. MutLγ (MLH1–MLH3 heterodimer) is a poorly understood member of the eukaryotic family of MutL proteins that has been implicated in triplet repeat expansion, but its action in this deleterious process has remained unknown. In humans, triplet repeat expansion is the molecular basis for ∼40 neurological disorders. In addition to MutLγ, triplet repeat expansion involves the mismatch recognition factor MutSβ (MSH2–MSH3 heterodimer). We show here that human MutLγ is an endonuclease that nicks DNA. Strikingly, incision of covalently closed, relaxed loop-containing DNA by human MutLγ is promoted by MutSβ and targeted to the strand opposite the loop. The resulting strand break licenses downstream events that lead to a DNA expansion event in human cell extracts. Our data imply that the mammalian MutLγ is a unique endonuclease that can initiate triplet repeat DNA expansions.

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DNA Repair and DNA Triplet Repeat Expansion: The Impact of Abasic Lesions on Triplet Repeat DNA Energetics

Journal of the American Chemical Society ◽

10.1021/ja902161e ◽

2009 ◽

Vol 131 (26) ◽

pp. 9354-9360 ◽

Cited By ~ 18

Author(s):

Jens Völker ◽

G. Eric Plum ◽

Horst H. Klump ◽

Kenneth J. Breslauer

Keyword(s):

Dna Repair ◽

Repeat Expansion ◽

Triplet Repeat ◽

Triplet Repeat Expansion ◽

Repeat Dna ◽

The Impact

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Dynamic DNA Energy Landscapes and Substrate Complexity in Triplet Repeat Expansion and DNA Repair

Biomolecules ◽

10.3390/biom9110709 ◽

2019 ◽

Vol 9 (11) ◽

pp. 709 ◽

Cited By ~ 2

Author(s):

Völker ◽

Plum ◽

Gindikin ◽

Breslauer

Keyword(s):

Dna Repair ◽

Excision Repair ◽

Repeat Expansion ◽

Triplet Repeat ◽

Energy Landscapes ◽

Abasic Site ◽

Triplet Repeat Expansion ◽

Dna Repeat ◽

Repeat Dna

DNA repeat domains implicated in DNA expansion diseases exhibit complex conformational and energy landscapes that impact biological outcomes. These landscapes include ensembles of entropically driven positional interchanges between isoenergetic, isomeric looped states referred to as rollamers. Here, we present evidence for the position-dependent impact on repeat DNA energy landscapes of an oxidative lesion (8oxodG) and of an abasic site analogue (tetrahydrofuran, F), the universal intermediate in base excision repair (BER). We demonstrate that these lesions modulate repeat bulge loop distributions within the wider dynamic rollamer triplet repeat landscapes. We showed that the presence of a lesion disrupts the energy degeneracy of the rollameric positional isomers. This lesion-induced disruption leads to the redistribution of loop isomers within the repeat loop rollamer ensemble, favoring those rollameric isomers where the lesion is positioned to be energetically least disruptive. These dynamic ensembles create a highly complex energy/conformational landscape of potential BER enzyme substrates to select for processing or to inhibit processing. We discuss the implications of such lesion-induced alterations in repeat DNA energy landscapes in the context of potential BER repair outcomes, thereby providing a biophysical basis for the intriguing in vivo observation of a linkage between pathogenic triplet repeat expansion and DNA repair.

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