Structural basis for recruitment of human flap endonuclease 1 to PCNA

Flap endonuclease- 1 ( FEN1) is a key enzyme for maintaining genomic stability and replication. Proliferating cell nuclear antigen ( PCNA) binds FEN1 and stimulates its endonuclease activity. The structural basis of the FEN1 PCNA interaction was revealed by the crystal structure of the complex between human FEN1 and PCNA. The main interface involves the C- terminal tail of FEN1, which forms two beta- strands connected by a short helix, the betaA -alphaA -betaB motif, participating in beta-beta and hydrophobic interactions with PCNA. These interactions are similar to those previously observed for the p21(CIP1/ WAF1) peptide. However, this structure involving the full- length enzyme has revealed additional interfaces that are involved in the core domain. The interactions at the interfaces maintain the enzyme in an inactive ' locked- down' orientation and might be utilized in rapid DNA- tracking by preserving the central hole of PCNA for sliding along the DNA. A hinge region present between the core domain and the C- terminal tail of FEN1 would play a role in switching the FEN1 orientation from an inactive to an active orientation.