Protein Ligase

PROTEIN LIGASE (E3s)

A ubiquitin ligase (also alleged an E3 ubiquitin ligase) is a protein that in aggregate with an E2 ubiquitin-conjugating agitator causes the adapter of ubiquitin to a lysine on a ambition protein via an isopeptide bond;

Ubiquitin-Protein Ligases : A variety of enzymes that collaborate with UBIQUITIN-CONJUGATING ENZYMES and ubiquitination-specific protein substrates. Each affiliate of this agitator accumulation has its own audible specificity for a substrate and ubiquitin-conjugating enzyme. Ubiquitin-protein ligases abide as both monomeric proteins multiprotein complexes.

Ubiquitin is accompanying to protein by a peptide band amid the C-terminal glycine of ubiquitin and epsilon amino groups of lysine residues in the protein these ligases abide both as monomeric proteins and as multiprotein complexes.

E3s ubiquitin protein ligase enzymology:

ubiquitin ligases are ATP-dependent enzymes that activate the accumulation of a covalent band amid ubiquitin all-over intracellular proteins and added proteins, generally to mark the proteasomal abasement or carriage nonlysosomal destination. Ubiquitination requires consecutive activity of an activating agitator (E1), a conjugating agitator (E2) and ligase (E3). Ubiquitin binds to the protein by a peptide band amid the ubiquitin C-terminal glycine and lysine protein alpha-amino groups.

In enzymology, an ubiquitin-protein ligase (EC 6.3.2.19) is an agitator that catalyzes the actinic reaction

ATP + ubiquitin + protein lysine AMP + diphosphate + protein N-ubiquityllysine

The 3 substrates of this agitator are ATP, ubiquitin, and protein lysine, admitting its 3 articles are AMP, diphosphate, and protein N-ubiquityllysine.

This agitator belongs to the ancestors of ligases, accurately those basic carbon-nitrogen bonds as acid-D-amino-acid ligases (peptide synthases). The analytical name of this agitator chic is ubiquitin:protein-lysine N-ligase (AMP-forming). This agitator is aswell alleged ubiquitin-activating enzyme. This agitator participates in 3 metabolic pathways: ubiquitin advised proteolysis, parkinson's disease, and huntington's disease.

Target:

The E3 ubiquitin ligase targets specific protein substrates for abasement by the proteasome. In general, the ubiquitin ligase is complex in polyubiquitination: A additional ubiquitin is absorbed to the first, a third is absorbed to the second, and so forth. Polyubiquitination marks proteins for abasement by the proteasome.

However, there are some ubiquitination contest that are bound to mono-ubiquitination, in which alone a individual ubiquitin is added by the ubiquitin ligase to a substrate molecule. Mono-ubiquitinated proteins are not targeted to the proteasome for degradation, but may instead be adapted in their cellular area or function, for example, via bounden added proteins that accept domains able of bounden ubiquitin.

Further complicating matters, altered lysines on ubiquitin can be targeted by an E3 to accomplish chains. The a lot of accepted lysine is Lys48 on the ubiquitin chain. This is the lysine acclimated to accomplish polyubiquitin which is accustomed by the proteasome. However, Lys63 can aswell be used, and chains application this lysine are important for DNA repair, amidst added functions.

Ubiquitin-protein ligases (E3s) :

There are four aloft classes of ubiquitin ligases:

HECT-domain proteins;

U-box proteins;

monomeric RING feel proteins; and

multisubunit complexes that accommodate a RING feel protein .

HECT-domain E3s are altered in that Ub is transferred to a conserved cysteine balance of the E3 in a thiolester linkage, and again the E3 transfers the Ub to the substrate . This action as a covalent agent in the alteration of Ub is not begin in added classes of E3 proteins. The RING feel burden (Really Interesting New Gene) comprises eight cysteine or histidine residues that bind two Zn2+ ions in a cross-brace anatomy. The U-box is structurally agnate to the RING feel motif, but it does not bind Zn2+, instead, hydrogen bonds yield the abode of the Zn2+ in the anatomy. Monomeric RING feel E3s and U-box E3s bind to both the substrate and the E2 agitator. In multimeric RING feel complexes, the RING feel protein binds the E2 while added proteins in the circuitous bind the substrate. These multimeric complexes abatement into two classes: cullin-based complexes, and the APC/C (anaphase announcement complex/cyclosome), which contains the cullin-like protein APC2.

HECT-domain E3s in C.elegans as example:

There are nine genes in C. elegans that encode proteins with a HECT area. Of these genes, alone two accept been advised in detail: oxi-1 and wwp-1. oxi-1 was cloned as a gene whose announcement increases beneath oxidative accent. There is no empiric RNAi phenotype of oxi-1; however, the RNAi assay was not performed beneath top oxygen altitude if oxi-1 would be affected to be alive. wwp-1 encodes a conserved protein with HECT and WW domains, and its RNAi burning causes beginning accident with abnormal morphogenesis afterwards the breach date. Large-scale RNAi screens arise that RNAi burning of the HECT-domain gene D2085.4 produces sterility in the P0. The actual six HECT-domain genes were not associated with reproducible RNAi phenotypes

Structural model of HECT-domain E3 complex

U-box E3s & E4s

There are four genes in C. elegans that encode proteins with a U-box area . The C. elegans U-box protein CHN-1 is the homolog of beastly CHIP. CHIP binds to the chaperones Hsp70 and Hsp90 and functions as an E3 to abase misfolded protein. C. elegans CHN-1 aswell binds to the Hsp70 homolog HSP-1, suggesting a agnate action . Animals homozygous for a absent allele of chn-1 accept hardly lower breed sizes at 20oC, but contrarily arise normal. Consistent with a cellular role with calefaction shock proteins, chn-1 homozygotes are acute to heat-stress, announcement abecedarian arrest and accident at college temperatures.

C. elegans CHN-1 physically interacts with a added U-box protein, UFD-2 . UFD-2 is the ortholog of beginning aggrandize Ufd2, which functions as an E4 . As declared above, an E4 agitator catalyzes the addendum of ubiquitin chains on proteins that already accept one or a few conjugated Ub . Hoppe et al., begin