Protein Sorting and Modification Flashcards
what are the functions of post-translational modifications?
controls protein activation, guides protein transport, alters protein-protein or protein-DNA interactions, targets proteins for degradation
what is proteolytic cleavage and what are examples?
enzyme mediated removal or AA residues
ex. removal of start met
ex. removal of signal sequence
ex. removal of certain aa sequence to form an active protein
what is a zymogen?
inactive enzyme needing to be processed to become active
ex of zymogen?
hormones - many need to be cleaved from large protein to smaller active peptides
ex. proinsulin – insulin + Cpeptide (serum levels of C peptide evaluate amt of insulin produced)
what is phosphorylation?
removal or addition of phosphate group to either serine, threonine or tyrosine as an on/off switch
what are protein kinases?
enzymes to add phosphate grou[p
what are phosphatases?
enzyme to remove phosphate group
what is glycosylation?
addition of oligosaccharides to protein via glycosidic bond to the hydroxyl or amine group of AA side chain
where are O-linked glycosylated proteins added?
golgi
where are N-linked glycosylated proteins added?
ER
examples of acetylation?
lysines acetylated on histones (acetylated = relaxed, deacetylated = repressed)
what is myristoylation
myristoyl is added to N terminus at glycine residue resulting in protein association with intracellular vesicles
what is palmitoylation and prenylation?
addition of a lipid on cysteine side chain, the palmitoyl groups (C16) anchor proteins to cell surface
what other lipids are found on cell surface proteins used in regulation/cell signaling?
farnesyl (C15) and geranylgerany (C20)
what is hydroxylation?
addition of hydroxyl group to AA
clinical example of hydroxylation?
proline and lysine residues hydroxylated on alpha chains of collagen. mutation in the gene encoding the lysyl hydroxylase leads to form of ehlers danlos syndrome?
pathology of ehlers danlos syndrome?
mutations in gene encoding lysyl hydroxylase (less elasticity)
what is carboxylation and why is it important?
carboxyl groups added to glutamine residues by vitamin K dependent carboxylation reaction. is important modification for blood clotting factors
what is ubiquitination
addition of small polypeptide ubiquitin to a protein via a lysine residue to target proteins for degradation in the proteasome
what proteins/enzymes are synthesized in the Er and modified and sorted through the golgi
secretory proteins, resident ER proteins, lysosomal enzymes
signal sequences are important for transport where?
import into ER, retention in lumen of ER, import into mitochondria, import into nucleus, import into peroxisomes
what proteins are transported into the ER?
transmembrane proteins, proteins found in the lumen or the ER or other membrane bound organelles, secreted proteins
what is a signal sequence?
sequences that specify which organelle protein is targeted to
steps of recruitment of ribosome to the ER (for translation of resident ER/secreted proteins)
- ribosome begins translation mRNA, comes across ER signal sequence of hydrophobic/nonpolar AA via the signal-recognitition particle (SRP) which stalls translation
- the signal recognition particle is recognized by SRP-receptor on the cytosol side of ER membrane and the SRP-ribosome/RNA to the surface of the ER at the Sec61 complex
- translation continues through the translocator Sec61. this makes a “rough ER”
- protein snakes into translocator via signal sequence, as polypeptide is made, is being pushed down into ER. peptidase cleaves signal protein which allows mature protein to enter ER lumen and be properly folded by chaperone proteins
