Ben Van Houten, Ph.D.
University of Pittsburgh
NIEHS grantees found that a protein known as XPA bends DNA and pauses in response to DNA damage, revealing the location of damaged DNA and potentially promoting the recruitment of DNA repair proteins. Using single molecule experiments and imaging techniques, the researchers observed the biochemistry in a living cell, providing insight into a new damage sensor role for XPA.
XPA is known to play a role in nucleotide excision repair (NER), a type of DNA repair that removes a wide range of DNA lesions, including damage caused by ultraviolet light. However, how XPA contributes to NER and whether it has a role in recognizing damage is not well understood. The researchers used a new method to calculate the molecular weight of small proteins bound to DNA and tracked proteins involved in DNA repair in 3D using real-time single molecule imaging.
The findings suggested that different forms of XPA were associated with different phases of movement along DNA. XPA cycled through three distinct states on DNA: rapidly hopping over long distances of the DNA strand, slowly sliding over short ranges of DNA while bending local DNA regions, and pausing and forming complexes with bent DNA. XPA paused more frequently in the presence of more DNA damage.
According to the authors, their data are consistent with a model in which XPA bends DNA to search for lesions and pauses in response to DNA damage, signaling the location of damaged DNA to promote recruitment of additional proteins to repair the DNA.
Citation: Beckwitt EC, Jang S, Detweiler IC, Kuper J, Sauer F, Simon N, Bretzler J, Watkins SC, Carell T, Kisker C, Van Houten B. 2020. Single molecule analysis reveals monomeric XPA bends DNA and undergoes episodic linear diffusion during damage search. Nature Commun 11(1):1356.