Ubiquitin Structure & Function: Difference between revisions
From Proteopedia
Jump to navigationJump to search
No edit summary |
No edit summary |
||
| Line 6: | Line 6: | ||
Ubiquitin can not only be found in the nucleus, but in the cytoplasm and cell-surface membrane as well. | Ubiquitin can not only be found in the nucleus, but in the cytoplasm and cell-surface membrane as well. | ||
One interesting characteristic of ubiquitin is its stability. Ubiquitin is able to withstand a range of pH levels and temperatures and is very resistant to tryptic digestion, while still containing seven Lysine and four arginine residues. Many aspects of ubiquitin's structure aid in this durability. Ubiquitin contains a hydrophobic core. Three hydrophobic residues found on the α-helix and 11 of the 13 hydrophobic residues from the β-sheet are involved in constructing this hydrophobic core. The main contributor to the ubiquitin stability is the vast amount of hydrogen-bonding interactions observed. The whole structure of ubiquitin undergoes significant hydrogen bonding, aside from the COOH terminus. | One interesting characteristic of ubiquitin is its stability. Ubiquitin is able to withstand a range of pH levels and temperatures and is very resistant to tryptic digestion, while still containing seven Lysine and four arginine residues<ref name="2.8Aref">PMID: 2987935</ref>. Many aspects of ubiquitin's structure aid in this durability. Ubiquitin contains a hydrophobic core. Three hydrophobic residues found on the α-helix and 11 of the 13 hydrophobic residues from the β-sheet are involved in constructing this hydrophobic core. The main contributor to the ubiquitin stability is the vast amount of hydrogen-bonding interactions observed. The whole structure of ubiquitin undergoes significant hydrogen bonding, aside from the COOH terminus. | ||
[[image:lysubq.png| thumb |right | upright=2.0 |Ubiquitin structure with lysine residues highlighted in Yellow.]] | [[image:lysubq.png| thumb |right | upright=2.0 |Ubiquitin structure with lysine residues highlighted in Yellow.]] | ||
Secondary structures found throughout the ubiquitin structure include three and one half turns of α-helix, a short 3<sub>10</sub> helix, a mixed β-sheet with five strands and seven reverse turns. Several unusual secondary structures are also seen including parallel G1 β-bulge, two reverse Asx turns and a symmetrical hydrogen-bonding region between two helices and two reverse turns. | |||
=Function= | =Function= | ||
At first, ubiquitin was believed to be a hormone involed in inducing the differentiation of lymphocytes and activating adenylate cyclase <ref name="2.8Aref" | At first, ubiquitin was believed to be a hormone involed in inducing the differentiation of lymphocytes and activating adenylate cyclase <ref name="2.8Aref"/>. However, today, ubiquitin is primarily known for its role in intracellular ATP-dependent protein degradation. This is accomplished through the process of several seperate reactions: | ||
=== Activation === | === Activation === | ||
The first step of ubiquitin activation involves the formation of a ubiqiotin-adenylate intermediate. This reaction requires an E1 ubiquitin-activating enzyme. The second step of ubiquitin activation transfers ubiquitin to the E1 active site cysteine residue and AMP is released. This step results in a thioester linkage between the C-terminal carboxyl group of ubiquitin and the E1 cysteine sulfhydryl group. | The first step of ubiquitin activation involves the formation of a ubiqiotin-adenylate intermediate. This reaction requires an E1 ubiquitin-activating enzyme. The second step of ubiquitin activation transfers ubiquitin to the E1 active site cysteine residue and AMP is released. This step results in a thioester linkage between the C-terminal carboxyl group of ubiquitin and the E1 cysteine sulfhydryl group. | ||
