Regulation of protein activity Flashcards
Cell identity is defined by its
proteome
Different cell types contain the same genome, but they express different RNAs and proteins
gene to mRNA–> alternative promotors, alternative splicing, RNA editing
mRNA to protein –> folding, degradation, co and post translational modification
what is proteome?
: a set of proteins produced in an organism, system
or biological context
Regulation is effected at multiple levels: name them.
- Chromatin structure and methylation
- Transcription regulators
- RNA processing
- RNA transport
- Translation
- mRNA degradation
- Protein activity
Post-translational Events
As the polypeptide chain forms, it folds into its three dimensional shape
– Some spontaneously
– Some need helper proteins called chaperones
Hydrophobic parts inside
What is the role of chaperones?
Assisted folding: the role of chaperones
Chaperones recognize hundreds of different non-native or misfolded polypeptides by their hydrophobic surfaces
Chaperones prevents aggregation of misfolded
or denatured proteins
acts an isolation cell and provides a favorable environment for gentle folding
What happens if incorrect folding is not death by the cell and what is the mechanism that deal with it?
protein aggregation —> cell death disease
Protein levels are regulated by targeted degradation: the role of the proteasome
incompletely folded protein and digested by proteasome –> loss of protein
The Proteasome
• The Proteasome – cap recognizes and binds polyubiquitinated proteins – polyubiquitinated is hydrolyzes , unfolds the proteins – degrades the target to peptides 3-25aa long • ATP driven • Proteolytic activity (processive)
Fate of newly synthesized proteins
proteins can move between compartment in different ways
What happens if it takes too long for the chaperons to correctly fold the incorrectly folded protein
it’s degraded by proteasome
Parts of the proteasome
Cap- recognizes and bind to the polyubiquitinated proteins Central cylinder (proteas )
How can protein move between compartments
cytosol to nucleus –> gated transport (selective gate)
cytosol to ER, mitochondria and etc… –>transmembrane transport (protein translocators)
from ER to the other compartment= vesicular transport
The signal that act as a post code is the amino acid sequence of the protein
Signal sequence for import into nucleus
nuclear localization sequence NLS
predominantly Lys —> positively charged
Signal for export from the nucleus
Nuclear export (NES)
Import into ER
contains many hydrophobic amino acid
How do proteins move from Cytosol to ER?
A Signal-Recognition Particle (SRP) Directs the ER Signal Sequence to a Specific Receptor in the Rough ER Membrane
Signal sequence of growing peptide binds to the signal recognition particle
binding of SRP to signal peptide causes a pause in translation
The ribosome-SRP complex binds to the SRP receptor on ER which causes the ribosome to bind to the translocator and translation continue and translocation begins
What cleaves the peptides from the ribosome in ER?
signal peptidase
What happens to the protein in post-translational modification in ER?
- glycosylated
* stabilised by disulfide bonds
glycosylation of the protein in ER
• addition of a common oligosaccharide
• covalently attached to the side chain of an
asparagine residue (N-linked)
• may be required for folding, stability and
function
how protein is stabilised by disulfide bonds?
stabilised by disulfide bonds
• covalent bond between 2 cysteine side chains
• intra- or inter-molecular crosslinks
• requires oxidative condition
Post-translational activation
• Covalent modifications of proteins after translation may include:
– Proteolysis (cleavage of the protein), e.g. activation of digestive enzyme
– Glycosylation (addition of sugars),e.g. blood group antigens
– Phosphorylation (addition of phosphate groups).e.g. receptor kinase substrate
• Such modifications are often essential to the final functioning of the protein.
Examples of chemical modifications of proteins and their function
Acetyl on Lys–> Helps to activate genes in chromatin by modifying histones
Ubiquitin on Lys –> Monoubiquitin addition regulates the transport of membrane proteins in vesicles
Polyubiquitin chain targets a protein for degradation
How different addition of Ubiquitin effect the protein?
Monoubiquitylation —> histone regulation
Multiubiquitylation –> endocytosis
Polyubiquitylation–> Proteasome degradation or DNA repair
Ubiquitin– depending on different binding of the molecules to each other their fate can be changed
Importance of post-translation modification
important role in regulating protein activity and protein levels
Post-translational modifications forma regulatory protein code
Two ways of activating the activity of proteins:
covalent phosphorylation (proteins kinase and proteins phosphatase) or non-covalent binding of GTP facilitated by another protein (GEF)( Guanine nucleotide exchange factor and GTPase activator protein) protein bound to GTP activated
