B2.024 Protein Life Cycles Flashcards
when do a large percent of normal proteins misfold?
after translation
what is the two fold effect of cytoplasmic crowding?
retards unfolding but enhances aggregation
what are protein denaturing conditions?
pH, ionic strength, pressure, temperature, osmotic pressure, urea
discuss protein unfolding in digestion
extreme acidity in the stomach unfolds proteins that have been consumed
what is a characteristic of pathological protein folding?
B sheet fibers, amyloid
how many proteins form amyloid?
> 21
what is amyloidosis from dialysis?
proteins sensitive to dialysis form amyloid and deposit in the patient’s body
how does ligand binding affect folding?
biases toward folded form in equilibrium
what are osmolytes?
nonspecific effect on all encountered proteins, induce solvation effects that increase folding
what are examples of osmolytes?
free amino acids, polyols, methylamines
how do kidney cells adapt to special stress?
can have high urea and NaCl concentrations, conditions change over time, compensate by changing sorbitol, betaine, inositol, glycerolphosphoryl choline
what makes the ER a special environment for protein folding and processing?
synthesis of secreted proteins, some lysosomal enzymes, integral membrane proteins
what two factors increase protein stability?
oxidizing w/ disulfide bonds
glycosylation
how are covalent osmolytes thought to work?
encourage protein folding bc proteins would rather fold than interact w osmolytes, preferential solvation
what is an example of a protein than can survive digestion?
ovomucoid, major egg white allergen
what are chaperone proteins?
heat shock proteins that are upregulated in stressful conditions, they fold new proteins, refold misfolded proteins, transport across membranes, and control activities of some proteins
what is the chaperonin pathway?
protein binds to chaperonin
ATP allows lid to close on chaperonin w protein inside
protein remodeling occurs inside
remodeled protein emerges
how many amino acids can fit in a chaperonin cavity?
450, 50 kD
how much protein degradation each day is normal?
1-2% turnover
what are 3 primary reasons for protein degradation?
cellular change, functional regulation, adverse conditions
what are the two protein degradation pathways and how do they differ?
proteasome: used with short half life proteins with transient functions that are abnormal or damaged
lysosome: used with long half life proteins used for housekeeping functions or in membranes
what are the two types of lysosomal degradation?
autophagy and chaperone mediated autophagy
characterize autophagy
nonselective, slow, constitutive
characterize chaperone mediated autophagy
selective, 30% of cytosolic proteins, hsc73 binding to “KFERQ” motifs, unfolded protein transported into the lysosome
what are the functional molecules in the lysosome?
> 12 cathepsin proteases
broad, overlapping substrate specificities
no apparent order to proteolysis
what is a proteasome?
large protein complex, not an organelle
what is the proteasome pathway?
misfolded protein gets tagged with ubiquitin
protein binds to proteasome
addition of ATP allows proteasome to degrade protein and recycle ubiquitin
describe the ubiquitin tagging process
E1- activator protein, ATP required
E2- several carrier isoforms
E3- recognizes both ubiquitin and target protein
how does ubiquitin bind to a protein?
peptide/amide bond between Ubq C-terminus and the lysine side chain of the protein
how does poly-ubq form?
bind at internal ubq lysines
what is the active site on a proteasome?
Asp-Thr-His
what is the outcome of protein turnover?
75% of free amino acids recycles
25% amino acids metabolized
-nitrogen excreted as urea
-carbon compounds burned for energy
what types of stress occur in the ER?
unfolded proteins in ER ROS of UV damage low amino acids heat hypoxia high free fatty acids
what is BiP?
a chaperone that senses stress
normally binds sensor proteins, unfolded proteins “soak up” Bip, thus releasing sensor proteins, becoming active
what are cellular responses to ER stress?
- inhibit global translation
- activate transcription/translation of
- ERAD proteins
- chaperones
- amino acid transporters
- oxidative stress protection
what is an example of protein degradation backfiring?
in cystic fibrosis the F508 deletes one aa in a protein, this causes the protein to fold slowly, the protein is degraded before it can function
