POST-TRANSLATIONAL PROTEIN MODIFICATION Flashcards
what is the lowest and most state shape for proteins?
their final 3D conformation
what develops before the tertiary structure?
Small regions of relatively stable secondary structure
what does tertiary folding result in?
fibrous or globular protein
what are proproteins?
inactive peptides or proteins
that need post-translational modifications to activate them
give an example of pro-forms of protein
production of insulin
how is insulin produced?
Ribosomes feed the growing AA chain (preproinsulin) directly into the ER where the signal peptide is immediately cleaved off by a signal peptidase to yield proinsulin. This is later processed further to mature and active insulin.
what is the 1st Post-translation modification event?
Cleavage and removal of signal peptide by signal peptidase in ER.
what is the 2nd Post-translation modification event?
Oxidation of -SH groups to -S-S- (disulphide bridges) in ER. This cross-links specific regions via the -S-S- covalent bond.
what is the 3rd Post-translation modification event?
Cleavage and removal of the C chain in ER.
what can Post-translational modifications involve?
processing
covalent modification
what is processing?
proteolytic cleavage to an active form
what is covalent modification?
the chemical modification of a protein after its translation
what happens during translation?
a polypeptide chain containing up to 20 genetically encoded AA is synthesized
what does covalent modification allow?
allow to significantly extend the structural repertoire of proteins
what do the changes in chemical structure of a protein lead to?
leads to the change in its spatial structure and biological activity
what does PTM’s of proteins being reversible allow?
allows rapid dynamic regulation of a protein activity by controlling the balance of reversible PTMs
what does the control of PTMs of proteins allow?
allow the control of their activity. This principle is widely used in nature to regulate numerous biological processes
what biological processes are controlled by PTM?
metabolism, cellular signaling, gene transcription
what is PTMs and de-modifications of proteins catalysed by?
by enzymes that are involved in the regulation of their target protein activity
what are PTM’s a key mechanism for?
to increase proteomic diversity
where does proteolytic cleavage occur?
at a peptide bond
wat occurs during proteolytic cleavage?
One or several AA could be removed from N-terminus of a protein, or protein peptide bond could be cleaved in the internal part of the protein
what is proline isomerisation?
the change in proline residue spatial conformation (transition between cis- and trans- conformations of peptide bonds involving proline)
what can proline isomerisation affect?
Can seriously affect protein structure adopted
what do PTMs involve the addition of?
small functional groups
give examples of functional groups added to PTMs
Phosphorylation
Acetylation
Methylation
Hydroxylation
what is protein phosphorylation?
process in which phosphate group, donated by ATP, is transferred to an acceptor protein
what catalyses the protein phosphorylation reaction?
protein kinase
is protein phosphorylation reversible or irreversible?
reversible
what is protein de-phosphorylation catalysed by?
protein phosphatase
what is pyruvate dehydrogenase regulated by?
by phosphorylation/ dephosphorylation by a protein kinase
what is protein kinase activated and inhibited by for pyruvate dehydrogenase?
activated by high [NADH]:[NAD+] and [acetylCoA]: [CoA], but inhibited by pyruvate
what is the cell cycle controlled by?
cyclins and their cyclin dependent kinases CDKs
what is the most commonly phosphorylated AA?
Serine followed by threonine
what does tyrosine phosphorylation lead to?
binding of specific proteins that promote protein:protein interactions as part of the signaling networks
how do you detect phosphorylated proteins?
Phospho-specific antibodies
2-Dimension Phosphopeptide
mapping with 32 P
what is protein acetylation?
process in which acetyl group, donated by acetyl Coenzyme A, is transferred to an acceptor amino acid, lysine, in protein
what is protein acetylation catalysed by?
by a Protein AcetylTransferase (PAT)
what is protein deacetylation catalysed by?
Protein DeACetylase (PDAC)
what is the most characterized targets of protein acetylation?
histones
what are the histone PATs and PDACs called?
histone acetyltransferases (HATs) and histone deacetylases (HDACs)
what does the reversible histone acetylation control?
gene transcription
what is protein methylation?
process in which methyl group, donated by S-adenosylmethionine, is transferred to an acceptor protein
what is protein methylation catalysed by?
protein methyltransferase
what is protein demethylation catalysed by?
protein demethylase
what are the 2 major amino acids methylated?
Arginine and Lysine
give an example of protein methylation
N- methylation of lysine and arginine side chains of histones involved in gene regulation
what is the histone code hypothesis?
multiple histone modifications, acting in a combinatorial or sequential manner on one/mulitple histone N-terminal tails specify unique downstream functions
what is citrullination?
deimination of arginine converting it to citrulline
what does the immune system do to citrullinated proteins?
attacks citrullinated proteins, and is implicated as a cause in auto-immune and arithritis diseases
what is glycosylation?
addition of mono- and oligo- saccharides
what large FG can be added to PTMs?
addition of other peptides or proteins (mono- and poly ubiquitination, SUMOylation)
addition of fatty acid and lipid residues
what is protein glycosylation?
process of adding mono- or poly- saccharides to a protein
what are glycoproteins?
Glycosylated proteins
what does protein glycosylation have an effect on?
on protein conformation, distribution, stability and activity
what biological functions does glycosylation have an effect on?
control of protein stability, trafficking and recognition
what are major structural components of many cell surface and secreted proteins?
Carbohydrates in the form of aspargine-linked (N-linked) or serine/threonine-linked (O-linked) oligosaccharides
where does N-linked and O-linked glycosylation take place?
in the ER
and Golgi apparatus
what is N-linked glycosylation?
Polysaccharide is added as a 14
sugar unit to asparagine residue of the newly synthesised polypeptide in the ER.
what is O-linked glycosylation?
Sugar added one in a time in Golgi, or in cytoplasm. The sugar is added usually to hydroxyl- group of serine or threonine. In some proteins hydroxy-
lysine or hydroxyproline are glycosylated
what proteins are in the golgi?
secreted proteins
what proteins are in cytoplasm?
cellular proteins
give examples of types of glycosylation
N-glycosylation O-glycosylation Glypiation C-glycosylation Phosphoglycosylation
how can glycosidic bonds be categorised into groups?
based on the nature of the sugar–peptide bond and the oligosaccharide attached
what is ubiquitin?
small protein containing 76 a.a.
what is the last glycine in ubiquitin attached to?
to lysine in proteins
what does the Attachment of mono-ubiquitin to a protein do?
plays multiple biological functions by changing the protein structure
what is polyubiquitination?
Attachement of polyubiquitin chain
what does polyubiquitination do?
to a protein marks the protein for degradation in a proteasome
what 3 types of enzymes are requires for ubiquitination?
ubiquitin- activating enzymes, ubiquitin conjugating and ubiquitin ligase enzymes (E1, E2 and E3 respectively)
what remove ubiquitin from proteins?
Deubiquitinating enzymes (DUBs)
what are proteasome?
large protein complexes inside all eukaryotes, arches and some bacteria
what is the function of proteasomes?
to degrade and unneeded or damaged proteins
what are the biological functions of the protein polyubiquitination and proteasomal degradation?
Removal of damaged/ mis-folded proteins
Control the lifespan of different proteins
Control the multiple cellular processes
how can you control cellular processes?
by regulating the availability of key regulatory proteins in these processes
what does ubiquitination control?
neuronal excitability and synaptic transmission
what is lipidation?
a method to traget proteins to membranes in organelles, vesicles and the plasma membrane
what are the 4 types of lipidation?
C-terminal glycosyl phosphatidylinositol (GPI) anchor
N-terminal myristoylation
S-myristoylation
S-prenylation
what does each modification of lipidation allow?
gives proteins distinct membrane affinities and increase the hydrophobicity of a protein
are the different types of lipidation mutually exclusive?
they’re not mutually exclusive, in that 2 or more lipids can be attached to a given protein
why are defects in protein post-traslational modifications and cell signaling important?
they are crucial in pathobiology of numerous diseases
what are enzymes controlling PTMs often used as?
as therapeutic targets
