| Type: | Conserved_site | Name: | Endonuclease III-like, iron-sulphur cluster loop motif |
| Description: | Endonuclease III () is a DNA repair enzyme which removes a number of damaged pyrimidines from DNA via its glycosylase activity and also cleaves the phosphodiester backbone at apurinic / apyrimidinic sites via a beta-elimination mechanism [, ]. The structurally related DNA glycosylase MutYrecognises and excises the mutational intermediate 8-oxoguanine-adenine mispair []. The 3-D structures of Escherichia coliendonuclease III [] and catalytic domain of MutY [] have been determined. Thestructures contain two all-alpha domains: a sequence-continuous, six-helix domain (residues 22-132) and a Greek-key, four-helix domain formed by one N-terminal and three C-terminal helices (residues 1-21 and 133-211) together with theFe4S4 cluster. The cluster is bound entirely within the C-terminal loop by four cysteine residues with a ligation pattern Cys-(Xaa)6-Cys-(Xaa)2-Cys-(Xaa)5-Cys which is distinct from all other known Fe4S4 proteins. This structural motif isreferred to as a Fe4S4 cluster loop (FCL) []. Two DNA-binding motifs have been proposed, one at either end of theinterdomain groove: the helix-hairpin-helix (HhH) and FCL motifs. The primary role of the iron-sulphur cluster appears to involve positioning conserved basic residues for interaction with the DNA phosphate backbone by forming the loop ofthe FCL motif [, ]. The iron-sulphur cluster loop (FCL) is also found in DNA-(apurinic or apyrimidinic site) lyase, a subfamily of endonuclease III. The enzyme has both apurinic and apyrimidinic endonuclease activity and a DNA N-glycosylase activity. It cuts damaged DNA at cytosines, thymines and guanines, and acts on the damaged strand 5' of the damaged site. The enzyme binds a 4Fe-4S cluster which is not important for the catalytic activity, but is probably involved in the alignment of the enzyme along the DNA strand. | Short Name: | Endouclease3_FeS-loop_motif |
