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QuickView for Zinc finger, RING-type, conserved site (biogroup)
- Description:
- Zinc finger (Znf) domains are relatively small protein motifs which contain multiple finger-like protrusions that make tandem contacts with their target molecule. Some of these domains bind zinc, but many do not; instead binding other metals such as iron, or no metal at all. For example, some family members form salt bridges to stabilise the finger-like folds. They were first identified as a DNA-binding motif in transcription factor TFIIIA from Xenopus laevis (African clawed frog), however they are now recognised to bind DNA, RNA, protein and/or lipid substrates. Their binding properties depend on the amino acid sequence of the finger domains and of the linker between fingers, as well as on the higher-order structures and the number of fingers. Znf domains are often found in clusters, where fingers can have different binding specificities. There are many superfamilies of Znf motifs, varying in both sequence and structure. They display considerable versatility in binding modes, even between members of the same class (e.g. some bind DNA, others protein), suggesting that Znf motifs are stable scaffolds that have evolved specialised functions. For example, Znf-containing proteins function in gene transcription, translation, mRNA trafficking, cytoskeleton organisation, epithelial development, cell adhesion, protein folding, chromatin remodelling and zinc sensing, to name but a few. Zinc-binding motifs are stable structures, and they rarely undergo conformational changes upon binding their target. A number of eukaryotic and viral proteins contain a conserved cysteine-rich domain of 40 to 60 residues (called C3HC4 zinc-finger or 'RING' finger) that binds two atoms of zinc. There are two different variants, the C3HC4-type and the C3H2C3-type, which is clearly related despite the different cysteine/histidine pattern. The latter type is sometimes referred to as "RING-H2 finger". The 3D structure of the zinc ligation system is referred to as the "cross-brace" motif. This atypical conformation is also shared by the FYVE (see <db_xref db="PROSITEDOC" dbkey="PDOC50178"/>) and PHD (see <db_xref db="PROSITEDOC" dbkey="PDOC50016"/>) domains. Many proteins containing a RING finger play a key role in the ubiquitination pathway. The ubiquitination pathway generally involves three types of enzyme, know as E1, E2 and E3. E1 and E2 are ubiquitin conjugating enzymes. E1 acts first and passes ubiquitin to E2. E3 are ubiquitin protein ligases, responsible for substrate recognition. It has been shown that several RING fingers act as E3 enzymes in the ubiquitination process.
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