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POST-TRANSLATIONAL PROTEIN MODIFICATION Flashcards

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1
Q

what is the lowest and most state shape for proteins?

A

their final 3D conformation

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2
Q

what develops before the tertiary structure?

A

Small regions of relatively stable secondary structure

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3
Q

what does tertiary folding result in?

A

fibrous or globular protein

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4
Q

what are proproteins?

A

inactive peptides or proteins

that need post-translational modifications to activate them

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5
Q

give an example of pro-forms of protein

A

production of insulin

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6
Q

how is insulin produced?

A

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.

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7
Q

what is the 1st Post-translation modification event?

A

Cleavage and removal of signal peptide by signal peptidase in ER.

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8
Q

what is the 2nd Post-translation modification event?

A

Oxidation of -SH groups to -S-S- (disulphide bridges) in ER. This cross-links specific regions via the -S-S- covalent bond.

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9
Q

what is the 3rd Post-translation modification event?

A

Cleavage and removal of the C chain in ER.

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10
Q

what can Post-translational modifications involve?

A

processing

covalent modification

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11
Q

what is processing?

A

proteolytic cleavage to an active form

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12
Q

what is covalent modification?

A

the chemical modification of a protein after its translation

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13
Q

what happens during translation?

A

a polypeptide chain containing up to 20 genetically encoded AA is synthesized

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14
Q

what does covalent modification allow?

A

allow to significantly extend the structural repertoire of proteins

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15
Q

what do the changes in chemical structure of a protein lead to?

A

leads to the change in its spatial structure and biological activity

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16
Q

what does PTM’s of proteins being reversible allow?

A

allows rapid dynamic regulation of a protein activity by controlling the balance of reversible PTMs

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17
Q

what does the control of PTMs of proteins allow?

A

allow the control of their activity. This principle is widely used in nature to regulate numerous biological processes

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18
Q

what biological processes are controlled by PTM?

A

metabolism, cellular signaling, gene transcription

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19
Q

what is PTMs and de-modifications of proteins catalysed by?

A

by enzymes that are involved in the regulation of their target protein activity

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20
Q

what are PTM’s a key mechanism for?

A

to increase proteomic diversity

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21
Q

where does proteolytic cleavage occur?

A

at a peptide bond

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22
Q

wat occurs during proteolytic cleavage?

A

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

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23
Q

what is proline isomerisation?

A

the change in proline residue spatial conformation (transition between cis- and trans- conformations of peptide bonds involving proline)

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24
Q

what can proline isomerisation affect?

A

Can seriously affect protein structure adopted

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25
what do PTMs involve the addition of?
small functional groups
26
give examples of functional groups added to PTMs
Phosphorylation Acetylation Methylation Hydroxylation
27
what is protein phosphorylation?
process in which phosphate group, donated by ATP, is transferred to an acceptor protein
28
what catalyses the protein phosphorylation reaction?
protein kinase
29
is protein phosphorylation reversible or irreversible?
reversible
30
what is protein de-phosphorylation catalysed by?
protein phosphatase
31
what is pyruvate dehydrogenase regulated by?
by phosphorylation/ dephosphorylation by a protein kinase
32
what is protein kinase activated and inhibited by for pyruvate dehydrogenase?
activated by high [NADH]:[NAD+] and [acetylCoA]: [CoA], but inhibited by pyruvate
33
what is the cell cycle controlled by?
cyclins and their cyclin dependent kinases CDKs
34
what is the most commonly phosphorylated AA?
Serine followed by threonine
35
what does tyrosine phosphorylation lead to?
binding of specific proteins that promote protein:protein interactions as part of the signaling networks
36
how do you detect phosphorylated proteins?
Phospho-specific antibodies 2-Dimension Phosphopeptide mapping with 32 P
37
what is protein acetylation?
process in which acetyl group, donated by acetyl Coenzyme A, is transferred to an acceptor amino acid, lysine, in protein
38
what is protein acetylation catalysed by?
by a Protein AcetylTransferase (PAT)
39
what is protein deacetylation catalysed by?
Protein DeACetylase (PDAC)
40
what is the most characterized targets of protein acetylation?
histones
41
what are the histone PATs and PDACs called?
histone acetyltransferases (HATs) and histone deacetylases (HDACs)
42
what does the reversible histone acetylation control?
gene transcription
43
what is protein methylation?
process in which methyl group, donated by S-adenosylmethionine, is transferred to an acceptor protein
44
what is protein methylation catalysed by?
protein methyltransferase
45
what is protein demethylation catalysed by?
protein demethylase
46
what are the 2 major amino acids methylated?
Arginine and Lysine
47
give an example of protein methylation
N- methylation of lysine and arginine side chains of histones involved in gene regulation
48
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
49
what is citrullination?
deimination of arginine converting it to citrulline
50
what does the immune system do to citrullinated proteins?
attacks citrullinated proteins, and is implicated as a cause in auto-immune and arithritis diseases
51
what is glycosylation?
addition of mono- and oligo- saccharides
52
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
53
what is protein glycosylation?
process of adding mono- or poly- saccharides to a protein
54
what are glycoproteins?
Glycosylated proteins
55
what does protein glycosylation have an effect on?
on protein conformation, distribution, stability and activity
56
what biological functions does glycosylation have an effect on?
control of protein stability, trafficking and recognition
57
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
58
where does N-linked and O-linked glycosylation take place?
in the ER | and Golgi apparatus
59
what is N-linked glycosylation?
Polysaccharide is added as a 14 | sugar unit to asparagine residue of the newly synthesised polypeptide in the ER.
60
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
61
what proteins are in the golgi?
secreted proteins
62
what proteins are in cytoplasm?
cellular proteins
63
give examples of types of glycosylation
``` N-glycosylation O-glycosylation Glypiation C-glycosylation Phosphoglycosylation ```
64
how can glycosidic bonds be categorised into groups?
based on the nature of the sugar–peptide bond and the oligosaccharide attached
65
what is ubiquitin?
small protein containing 76 a.a.
66
what is the last glycine in ubiquitin attached to?
to lysine in proteins
67
what does the Attachment of mono-ubiquitin to a protein do?
plays multiple biological functions by changing the protein structure
68
what is polyubiquitination?
Attachement of polyubiquitin chain
69
what does polyubiquitination do?
to a protein marks the protein for degradation in a proteasome
70
what 3 types of enzymes are requires for ubiquitination?
ubiquitin- activating enzymes, ubiquitin conjugating and ubiquitin ligase enzymes (E1, E2 and E3 respectively)
71
what remove ubiquitin from proteins?
Deubiquitinating enzymes (DUBs)
72
what are proteasome?
large protein complexes inside all eukaryotes, arches and some bacteria
73
what is the function of proteasomes?
to degrade and unneeded or damaged proteins
74
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
75
how can you control cellular processes?
by regulating the availability of key regulatory proteins in these processes
76
what does ubiquitination control?
neuronal excitability and synaptic transmission
77
what is lipidation?
a method to traget proteins to membranes in organelles, vesicles and the plasma membrane
78
what are the 4 types of lipidation?
C-terminal glycosyl phosphatidylinositol (GPI) anchor N-terminal myristoylation S-myristoylation S-prenylation
79
what does each modification of lipidation allow?
gives proteins distinct membrane affinities and increase the hydrophobicity of a protein
80
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
81
why are defects in protein post-traslational modifications and cell signaling important?
they are crucial in pathobiology of numerous diseases
82
what are enzymes controlling PTMs often used as?
as therapeutic targets

IMS (52 decks)

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