Tandem MutSβ binding to long extruded DNA trinucleotide repeats underpins pathogenic expansions.

ABSTRACT: Expansion of trinucleotide repeats causes Huntington's disease, Fragile X syndrome and over twenty other monogenic disorders¹. How mismatch repair protein MutSβ and large repeats of CNG (N=A, T, C or G) cooperate to drive the expansion is poorly understood. Contrary to expectations, we find that MutSβ prefers to bind the stem of an extruded (CNG) hairpin rather than the hairpin end or hairpin-duplex junction. Structural analyses reveal that in the presence of MutSβ, CNG repeats with N:N mismatches adopt a B form-like pseudo-duplex, with one or two CNG repeats slipped out forming uneven bubbles that partly mimic insertion-deletion loops of mismatched DNA². When the extruded hairpin exceeds 40-45 repeats, it can be bound by three or more MutSβ molecules, which are resis

SUBMITTER: Li J 

PROVIDER: S-EPMC10760016 | biostudies-literature | 2023 Dec

REPOSITORIES: biostudies-literature