Two‐stage dynamic DNA quality check by xeroderma pigmentosum group C protein

Xeroderma pigmentosum group C (XPC) protein initiates the DNA excision repair of helix‐distorting base lesions. To understand how this versatile subunit searches for aberrant sites within the vast background of normal genomic DNA, the real‐time redistribution of fluorescent fusion constructs was monitored after high‐resolution DNA damage induction. Bidirectional truncation analyses disclosed a surprisingly short recognition hotspot, comprising ～15% of human XPC, that includes two β‐hairpin domains with a preference for non‐hydrogen‐bonded bases in double‐stranded DNA. However, to detect damaged sites in living cells, these DNA‐attractive domains depend on the partially DNA‐repulsive action of an adjacent β‐turn extension that promotes the mobility of XPC molecules searching for lesions. The key function of this dynamic interaction surface is shown by a site‐directed charge inversion, which results in increased affinity for native DNA, retarded nuclear mobility and diminished repair efficiency. These studies reveal a two‐stage discrimination process, whereby XPC protein first deploys a dynamic sensor interface to rapidly interrogate the double helix, thus forming a transient recognition intermediate before the final installation of a more static repair‐initiating complex.