XPG I protein domain

In molecular biology, the XPG-I is a protein domain found on Xeroderma Pigmentosum Complementation Group G (XPG) protein.^[1] The XPG protein is an endonuclease which repairs DNA damage caused by ultraviolet light (UV light). The XPG protein repairs DNA by a process called, Nucleotide excision repair. Mutations in the protein commonly cause Xeroderma Pigmentosum which often lead to skin cancer.

XPG_I
flap endonuclease-1 from Methanococcus jannaschii
Identifiers
Symbol	XPG_I
Pfam	PF00867
Pfam clan	CL0464
InterPro	IPR006086
PROSITE	PDOC00658
SCOP2	1a77 / SCOPe / SUPFAM
CDD	cd09868
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Function

The function of the internal XPG (XPG-I) domain contains many of cysteine and glutamate amino acid residues that are frequently found in various enzyme active sites, DNA nucleases. The I domain, together with the N-terminal forms the catalytic domain that contains the active site.^[2]

Mechanism

XPG cleaves the 5'-overhanging flap structure that is generated when DNA polymerase encounters the 5'-end of a downstream Okazaki fragment. It has both 5'endo-/exonuclease and 5'-pseudo-Y-endonuclease activities. Cleaves the junction between single and double-stranded regions of flap DNA. The endonuclease binds 2 magnesium ions per subunit, which probably participate in the reaction catalyzed by the enzyme. May bind an additional third magnesium ion after substrate binding.