3-Proteins Flashcards
(32 cards)
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.
What are some cellular processes regulated by protein degradation?
Gene transcription, cell cycle progression, organ formation, circadian rhythms, inflammatory response, tumor suppression, cholesterol metabolism, antigen processing.
What are some Hb properties?
- Composed of globin chains and heme
- Hb has 2 alpha and 2 beta chains
- HbA (adult), HbF (fetal alpha2-gamma2)
- 1 heme per chain
What is a heme group?
-It’s the non-protein part of Hb that contains an iron atom and a protoporphyrin IX ring.
-Atom iron is slightly outside the heme ring in deoxy-Hb, pulled there by a histidine
-O-binding initiates structural changes, iron moved into the same plane as the ring & His is pulled up
-
What are the two forms of Hb?
- Deoxy (T=taut): low affinity
- Oxy (R=relaxed): high affinity
- Orientations of alpha & beta chains differ
What is positive cooperativity?
- Difficult to bind O2 in T-form; becomes progressively easier as conformation switches to R-form. Binding thus accelerates.
- If no cooperativity was present, Hb would reach a max saturation only at very high pO2. Blood would be much less efficient at transporting O2 to tissues.
What is the Bohr affect?
- A decrease in pH (high CO2) lowers affinity for oxygen, and this facilitates its release. Shifts curve to the right.
- An increase in pH (low CO2) increases O2 affinity, picks up more O2. Shifts curve to the left.
What’s BPG’s effect on Hb binding of O2?
- It’s an effector, “assistant,” of Hb
- 2,3-BPG binds only when Hb is in the T (deoxy) form. Its binding stabilizes this form decreasing affinity for O2 -> more oxygen release
- W/o BPG, Hb would release 8% of its O to tissues
- Expelled when Hb picks up O2 in the lungs
- A single molecule of BPG binds to +cavity
- In the R (oxy) form, cavity collapses, no BPG
How is HbF different from HbA?
- Fetal Hb has a higher affinity for oxygen than adult Hb. This favors movement of O2 from maternal blood to fetal blood.
- HbF is on the left side of HbA curve.
What are some general characteristics of enzymes?
- Most are proteins (some RNA)
- Effective in small amounts
- Function in “mild” conditions
- Have specificity
- Can be highly regulated
- Often use cofactors
- Unchanged by reaction
- Utilizes ES complexes
- Lower activation energy of reactions
- Do not affect Keq of reaction
