Define post-translational modifications
- Covalent attachment (isopeptide bond) of a modifier protein after translation of mRNA in an enzymatic process
- Regulate proteome complexity (5% of proteome is enzymes for ptm)
What is the function of post-translational modifications?
- Ligand binding
- Trafficking
- Activation (e.g phosphorylation)
- Targetting for degradation
- Facilitating protein-protein interations
Define protein protein interactions
- Physical contact between two or more proteins (non-covalent)
- Can be transient or long-lived
- Underpin biochemical properties of proteins
- Combinations of hydrophobic bonding, salt bridges, van der waals forces and hydrogen bonds
What is the significance of SDS in a western blot?
- Give negative charge
- Prevent protein-protein interactions as it is a strong detergent (does not break covalent interactions)
What are the differences between SUMOylation and ubiquitin?
- E3s are not important and can be done without them
- Only one type of ubiquitin, different isoforms of sumo
- Potential for mono-SUMOylation bu SUMO-1 (can also act as chain terminator)
- Far reduced complexity of system (only 1 E1 and E2, only 4 x E3)
- Requires motif (consensus site) on target protein
How are the SUMO isoforms formed?
- Produced as longer precursor
- Cleaved at di-glycine, this glycine used to bond to target proteins on lysine
- SUMO2/3 are 97% identical
- SUMO 1 is 40% identiclal
What motif is common in proteins binding to SUMO?
FILMV motif (also contained by SUMO-2/3 but nor SUMO-1 which is why it cannot form a chain) - Proteins can contain multiple of these sites leading to them becoming heavily modified by SUMO
What is SUMO signalling involved in?
Implicated in almost every NUCLEAR process: facilitation of protein-protein interactions
- Nuclear pore regulation
- Transcription factor regulation
- Genomic stability
- Protein stability
- Anti-viral/pro-viral response
What is the typical SUMO-interacting motif?
- Hydrophobic domain surrounded by acidic residues (phosphorylation, also believed to mediate isoform specificity)
- Interacts with SUMO at its second beta sheet
What are PML Nuclear bodies?
- Found within the nuclei
- Heavily co-localised with SUMO
- Works as a recruitment domain for many different proteins and can be found around detected virus
How does SUMO aid the function of PML-NBs?
- Post translational modification of SUMO (PMLs have a SIM domain) to form a network and ensuing protein protein interactions to produce PML-associated proteins
- Often found on viruses in the nucleus
What is the difference between poly and multi SUMOylation?
poly - multi-SIM protein interacting with one SUMO
multi - multi-SIM protein interacting with many SUMOs
- Protein with multiple SIM domains can interact with many SUMO-modified proteins
Give an example of SUMO-Ub cross-talk?
- RNF4 is a SUMO-targetted ubiquitin ligase (E3 ligase)
- Protein that is poly-SUMOylated
- RNF4 multiple SIM domains, must bind to poly-sumoylayted protein to dimerize
- Can then target these proteins for degradation
- This is important for PMLs
What is acute promyelocytic leukaemia?
- Rare but devastating disease
- Cased by genomic transocation causing PML-RAR fusion
- Blocks normal myeloid differentiation program as fusion protein is thought to repress genes associated with differentiation
How could APL be treated?
- PML can interact with DNA, can be SUMOylated which can bring in proteins that act as transcription repressors, RAR also acts as a repressor
- Could be treated through the upregulation of SUMOylation of PML, target for degradation through RNF4 allowing genes to activate again
- Can be done through treatment with arsenic
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Lipids63
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Membrane Trafficking30
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Principles of Cell Signalling71
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Ion channels13
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Ras signalling13
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Glut4 translocation18
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Ubiquitination19
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Hippo pathway and cancer16
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Ca signalling19
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Plant transport51
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SUMO15
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Cell fractionation10
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Visualising gene expression and protein localisation13
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Western blotting11
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Willin21
