Exam 3- Post Translational Modifications Flashcards
What is dictates protein shape?
Folding + Post translational modifications
How is folding achieved?
Chaperons and Chaperonins
What are the three categories of post translational modifications
Non-Reversible
Seldom Reverted
Rapidly Reverted
What’s the non-reversible PTM
cleavage
once it is cut it cant be put back together
What are the seldom reverted PTM?
Carbs and Lipids
What are the rapidly reverted PTM
Phosphorylation
Ubiquitinylation
SUMOylation
Protein cleavage is frequent for what pathway?
For targeting from sec pathway.
Cut off signal sequence
Protein glycosylation occurs either at:
N link or O link
Where is N linked glycosylation
to an Asn residue 4 residues from the N term end
N-Glycosylation involves the transfer of a pre-formed chain made of 14 different sugars.
The vast majority of proteins that are translocated into the ER are CO-TRANSLATIONALLY N-Glycosylated.
Where is an O linked glycosylation
to Ser or Thr residue
O-Glycosylation involves the addition of one sugar at a time.
For N-glyco the removal of 3 glucose residues targets the protein where?
ER
For N-glyco the removal of 3 glucose residues, and removing mannose and adding other sugars targets the protein where?
to the Golgi
What does glycosylation do to proteins? Why is it important? Where in the cell are most N-Glycosylated proteins?
Adds sugars to proteins making them “sticky”, allowing them to play a role in cell adhesion and cell to cell communication.
What are the 3 types of lipid additions to proteins?
Myristoylation
Farnesylation
Palmitoylation
what is Myristoylation
adding 14 carbon myristic acid to N term glycine after removing Met 1
what is Myristoylation going to after?
inner face of plasma membrane
what is Farnesylation
adding 15 Carbon farnesyl acid to the 4 amino acid from the N term which is Cys’ Sulfur residue. Then cleaving the 3 AAs making Cys the terminal. Then adding ester group to the N term Carboxyl of Cys.
Which protein is farnesylated?
Ras Protein
Cancer cell growth
What is Palmitoylation
Adding 16 Carbon palmitolaic acid to the Cys reside in the middle of the chain.
What is Palmitoylation send the protein?
Cystolic face of the plasma membrane
What’s the main effect of lipidation on proteins?
Allows them to associate with membranes.
What’s a GPI anchor? How is it added to the protein? What’s the final topology and location of ALL GPI anchored proteins?
Added to the protein inside lumen of the ER at C-terminus.
Always targets proteins the extracellular side of the plasma membrane
ALL GPI proteins end up at PM and are facing the extracellular environment.
What is phosphorylation?
Attachment of phosphate group to the protein, through covalent association.
Causes conformational change in protein, altering its function.
Mediated by protein kinases.
Regulates the activity of enzymes involved in cellular metabolism.
What are the main residues that can be phosphorylated?
Serine and Threonine
Tyrosine
What’s a kinase?
enzyme that transfer phosphate groups from ATP to hydroxyl groups of the side chains of amino acids
Main types of kinases?
Serine and Threonine kinases
Tyrosine has its own kinase
What’s a phosphatase?
Enzyme that removes phosphate groups from proteins.
Is the active form of a protein always the phosphorylated one?
No phosphorylation can activate and deactivate
What is a signal transduction pathway?
The cascade of events triggered by a signal received at the plasma membrane – usually results in the transcription of a specific set of genes. Signal transduction pathways usually involve a series of phosphorylation and de-phosphorylation events.
How much does phosphorylation change the molecular weight?
1-4kD shift
What is Ubiquitin?
Ubiquitin is a small protein (only 76 amino acid residues long) that can be post-translationally conjugated to other proteins via iso-peptide links formed between the C-terminal glycine residue in Ubiquitin and the epsilon-amino group in Lysine residues located within the target protein to be Ubiquitinylated.
What is SUMO?
SUMO stands for Small Ubiquitin-like Modifier; hence, SUMO is a Ubiquitin-like protein that can also be post-translationally conjugated to other proteins in the same way as Ubiquitin.
Unlike ubiquitin SUMO has its N term exposed to interact as well as its C term
96 amino acids
added to Lysines
Does NOT target for degradation and does NOT form poly-SUMO chains
What’s the main effect mediated by the conjugation of Ubiquitin to a target protein?
Ubiquitinylation usually targets the modified protein to be degraded by the PROTEASOME. To do this, proteins need to be conjugated not with single Ubiquitin molecules but with long chains of Ubiquitin (poli-Ubiquitinylation).
what’s the PROTEASOME?
Protein shredder of the cell, can break down proteins into individual amino acids.
What’s the main effect mediated by the conjugation of SUMO to a target protein?
SUMO is a match maker - The protein can interact with other proteins it couldn’t interact with before, even after SUMO is removed.
effects associated with SUMOylation are changes in cellular localization, changes in the ability of the modified protein to establish specific protein-protein interactions, changes in the transcriptional activation power of transcription factors
Is the binding of small molecules to a protein a type of post-translational modification?
NO (because to be considered a post-translational modification the molecule added must be covalently associated to the protein) small molecules are not covalently attached, but the binding of small molecules to a protein can exert dramatic changes in protein shape and function.
What is allosteric regulation?
Regulation of enzyme activity by molecule binding at a site different from the enzymatically active site
2 examples of adding small molecules to proteins.
Binding of small molecules – exemplified by the binding of the heme group to the globin peptide producing hemoglobin,
and the binding of GTP to GTPases such as eIF2 and Ran. Small molecules can add extra functions to proteins.
What is feedback inhibition?
Involves a series of different enzymes. Final product made in the series, inhibits the activity of the very first enzyme (thereby controlling its own concentration)
