Proteostasis Flashcards
proteostasis
-protein and homeostasis
-coordinated cellular processes, regulating synthesis, folding, localization, and degradation of proteins
-regulates biological activities and health of cells
-consists of >1000 cellular components
protein coding review
primary structure= sequence of amino acids
secondary structure= alpha helices, beta strands
tertiary structure = fold helices and strands into domains
quaternary structure functional assemblies of chains (subunits)
molecular chaperones
-evolutionary ancient system
-prevents damaged or newly synthesized proteins from aggregating
-provides a microenvironment for refolding
-Molecular chaperones are a group of proteins that play a crucial role in assisting the proper folding, assembly, and stabilization of other proteins within a cell.
chaperones can help proteins to fold and refold to their ______ state?
Native
examples of molecular chaperones
Examples of well-known molecular chaperones include Hsp70 (Heat Shock Protein 70), which assists in the folding of nascent polypeptide chains, and Hsp90 (Heat Shock Protein 90), which is involved in the maturation and stabilization of a wide range of proteins, including many involved in cell signaling.
-HSP70 holds and releases hydrophobic segments of proteins
what are the protein misfolding states associated with neurodegenerative diseases?
amyloid fibrils, Amorphus aggregates, oligomers
true or false : chaperones lower the energy barriers to the native state and block the transition to undesired protein states
true!
chaperones facilitate protein folding in crowded cell
- there are over 200 chaperones to deal with the diversity of protein folding
-every cell contains approximately 2 billion protein molecules
-chaperones can make up to 10% of a cells protein content
correct protein folding slows as protein ____ increases
length
with increasing protein length: there are more non-native (incorrect) contacts and more intermediate states
misfolded proteins directed to degradation pathways
-30% of newly synthesized proteins are degraded
-incorrect translation
-improper folding - many check points for some proteins
-failure to attain correct localization or integration with other proteins/cell components
protein misfolding can also occur over time due to:
-inherent protein stability
-protein activity
-environmental stress
major degradation pathways
1) ubiquitin-proteasome system (UPS)
-central role in maintaining cellular proteostasis by removing damaged or unwanted proteins, regulating protein levels, and controlling various cellular processes.
Ubiquitination: a complex pathway for tagging proteins for degradation
-The process begins with the covalent attachment of a small protein called ubiquitin to the target protein to be degraded. This modification is carried out by a series of enzymes:
E1 (ubiquitin-activating enzyme) activates ubiquitin in an ATP-dependent reaction.
E2 (ubiquitin-conjugating enzyme) receives the activated ubiquitin from E1.
E3 (ubiquitin ligase) facilitates the transfer of ubiquitin from E2 to the target protein. E3 ligases are highly specific and determine which proteins are tagged for degradation.
proteasomes two major functions?
-rapid degradation of misfolded proteins
-controlling half-lives of proteins
features of the proteasome
- degrades up to 1/3 of newly synthesized proteins
-abundant ATP-dependent protease
-located in the cytosol
-consists of central cylinder (20s core) with 19s caps on each end
20S core/proteasome
-central hollow cylinder formed from multiple protein subunits
-assembled as a stack of 4-heptameric rings
-some subunits: distinct proteases, active sites face cylinder’s inner surface
-28 subunits (a7B7)
19S caps
-large protein complex
-17+ subunits (6 of which are ATPases)
-about 20 distinct proteins
-6 proteins hydrolyze ATP
-ATPases unfold proteins and move them into the 20s core for proteolysis
-primarily acts on ubiquitinated proteins
Ubiquitin
-76 aa protein
-contains 7 lysine residues
-polymerization of Ub occurs via Lys residues
-the function of Ub is different dependant on Lys residue used for polymerization
complexity of ubiquitination
E1= activating enzyme-, requires energy
E2 = conjugating enzyme, 30 structurally similar but distinct E2 enzymes
E3= ligase, 100’s of E3 enzymes, adds ubiquitin to protein
-humans have >500 E3 ligases
-E3 ligase largely determines the targeting of specific proteins
end result: targeting different degradation pathways
-UPS
-Autophagy pathways
Autophagy
“self-eating,” which accurately describes the process by which the cell digests its own components. Autophagy is essential for cell survival, adaptation to stress, and the removal of toxic protein aggregates
chaperone-mediated autophagy (CMA)
selective cellular process where specific proteins are targeted for degradation in lysosomes. Unlike general autophagy, which engulfs cellular components within autophagosomes, CMA involves the direct delivery of individual proteins to lysosomes. This process relies on chaperone proteins, such as Hsc70, that recognize specific target proteins with a CMA recognition motif.
intercellular proteostasis
maintenance of protein homeostasis or proper protein function not just within individual cells but also within a broader multicellular context, typically within a tissue or an organism. It involves mechanisms and processes that help ensure the correct folding, trafficking, and degradation of proteins not only within a single cell but also in interactions between neighboring cells
age-associated effects on proteostasis
-most neurodegenerative diseases show pathology involving specific and distinct protein misfolding events
Alzheimer’s disease protein is called?
amyloid beta
Tau
Amyotrophic lateral sclerosis protein is called?
TDP-43
FUS
