3-Proteins Flashcards
What determines how a protein is modified?
The nature of the modification is related to cellular localization and function. Can be reversible or not.
What are the two types of proteolysis modifications?
- Exo: removal of N-terminal (ex. initiator methionine excision)
- Endo: removal of peptide
What are some alpha-amino modifications?
Acetylation and myristoylation
What is the importance of N-terminus acetylation?
- 80% of human cytosolic proteins are acetylated at teh N-terminus
- Stability against degradation by aminopeptidase
- Protects from non-enzymatic glycation by reducing sugars
- N-terminal acetylation occurs co-translationally when ~50aa have been polimerized
- Acetyl group is donated by acetyl-CoA
How can protein modifications analysis give a diabetes diagnosis?
HbA is not N-acetylated, so it is susceptible to N-terminal glycation by the aldehyde group of isomerized glucose by a non-enzymatic reaction. It produces a minor variant HbA1c that can be identified.
What does kinase do?
It transfers gamma-phosphate from ATP to one of 3 amino acids (ser, tyr, thr)
What role does phosphorylation play in NFkB pathway?
- NFkB is a TF bound by IkB, which masks the nuclear localization signal of NFkB.
- Inflammation leads to activation of receptors that activate phosphorylation of IkB by IKK
- IkB is degraded, and NLS is unmasked
- NFkB translocates to the nucleus and activates transcription of its target
What are phosphatases?
Enzymes that remove phosphate groups. It’s a hydrolysis reaction.
What are some characteristics of Protein kinase A (PKA) ?
- Protein kinase A is a family of enzymes whose activity is dependent on cellular levels cAMP. -Functions: regulation of glycogen, sugar, and lipid metabolism.
- 4 polypeptide molecule, 2 regulatory and 2 catalytic subunits.
- Binding 4 cAMP molecules activates PKA by dissociating the holoenzyme into 2 R subunits and 2 catlytic subunits that are now active.
How does the insulin receptor work?
- Insulin receptor binds insulin
- Signaling activates a protein kinase cascade, phosphorylation of the receptor’s transmembrane domains.
- Phosphorylation in receptor acts as docking site for intracellular proteins with phosphorylated tyrosines like IRS-1 (interaction mediated by SH2 domains)
- PIP3-kinase then uses phosphorylation of IRS-1 as docking site
What is proteolytic processing? what is it used for?
- Removal of 1+ pro-peptides
- Mostly in secretory vesicles & occasionally extracellular
- Characteristic of many hormones, growth factors, hydrolytic enzymes
- To produce bioactive peptides
- Proteases involved are highly specific
What is proteolytic destruction?
- Involves recognition & tagging (ubiquitin, SUMO)
- Ubiquitin also regulates protein activity (may tell protein to change activity or interact with others)
- Proteins tagged with ubiquitin are degraded in the proteasome -> fragments + ubiquitin
How does ubiquitin get attached to proteins?
-Ubiquitin is 76 aa long
-There are 2 E1 proteins, 33 E2 proteins, >700 E3 proteins (these determine specificity)
1) Ub-ATP –E1 –> Ub-AMP
2) Ub-AMP –E1 –> Ub-E1
3) Ub-E1 –E2–> Ub-E2
4) Ub-E2 –E3–> (gets together target protein
and Ub-E2) –> Ub-target
What in a gel can help diagnose myeloma? why?
- A normal individual’s serum has a major albumin band, while myeloma patients have a very distinct band (an Ig) in addition to albumin.
- In myeloma patients, there is excess Ig in serum because of overproduction of plasma cells.
What is Velcade, and what is its mechanism of action?
- It’s a proteasome inhibitor to treat multiple myeloma, so it prevents protein degradation
- Myeloma cells are more sensitive than normal cells & this are killed more easily.
