| 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 MutY recognises and excises the mutational intermediate 8-oxoguanine-adenine mispair []. The 3-D structures of Escherichia coli endonuclease III [] and catalytic domain of MutY [] have been determined. The structures 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 the Fe4S4 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 is referred to as a Fe4S4 cluster loop (FCL) [ ]. Two DNA-binding motifs have been proposed, one at either end of the interdomain groove: the helix-hairpin-helix (HhH) region (see ) and FCL motif, described in this entry. 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 of the FCL motif [ , ]. | Name | Endonuclease III, iron-sulphur binding site |
| Short Name | Endouclease-III_FeS-bd_BS | Type | Binding_site |
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