Protein sorting II Flashcards
what are the 3 rules on transmembrane transport
- transmembrane translocator needed on target organelle
- proteins are kept unfolded to cross membrane
- localization signal is usually removed after sorting
what are the steps for protein sorting to the mitochondria
- localization signal at N-terminal of m-proteins
- cytosolic and m-chaperone proteins HSP7- family
- transmembrane translocators TIM and TOM
what kinds of proteins are sorted into the ER
soluble/secreted/transmembrane
how are proteins sorted to the ER
- localization signal peptide at N terminus of protein
- sorting occurs co-translationally
- localization to ER is mediated by SRP, SRP receptor and protein translocator
- localization signal is removed after sorting
what is SRP -signal recognition particle
is a ribonucleotide, it binds to the ER signal sequence and slows down translation, and directs polypeptide to ER
soluble proteins are released in the ER
lumen
transmembrane proteins are kept in the ER
membrane, they need another internal signal to be kept here, once inserted it cannot change its orientation
which proteins can leave the ER
properly folded
what 4 things occur in the ER
- protein folding
- disulfide bonds
- N-glycosylation
- assembly of protein complexes
improperly associated proteins are taken
to the cytosol where they are degraded
what is a proteasome
it is in the cytosol, it is not an organelle, it is a multiprotein complex, it recognizes and degrades poly-ubiquitinylated proteins, and needs ATP
how do cells decide how much ER they need
- an unfolded protein response is activated by an accumulation of misfolded/unfolded proteins in the ER lumen. A signal is sent from the ER to the nucleus to synthesize more ER components
what are the 4 consequences of a UPR
- reduce import of proteins in ER
- Increase ER folding, secretory, degradation capacity
- degrade unfolded proteins
- send cell to death
