Download Protein: Post-translational Modification

Protein: Post-translational Modification
林富邦老師
Gene encoding region (ORF)
↓transcription
mRNA
↓translation
Protein (nascent protein, precursor protein)
↓protein processing, post-translational modification
Mature protein
↓folding
Biological active protein
Post-translational Modification

1. numerous and diverse
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2. change the charge, conformation or size of
protein molecule
Effects of Post-translational Modification
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1. stability of protein
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2. biochemical activity (activity regulation)
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3. protein targeting (protein localization)
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4. protein signaling (protein-protein
interaction,cascade amplification)
Why protein post-translational modifications
are made? (Biological functions)
A. Regulation (interconvertable modifications)

Monocyclic cascade (allosteric effectors)
-P/de-P receptor-associated Tyr-Kinase coupled cascade

Cyclic cascade
ADP-ribosylation / poly-ADP-ribosylation
Coordinated Glycogen phosphorylase / Glycogen synthase
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Unidirectional cascade
Proteolytic activation
B. Cross-links
Stabilize or fix certain folded str. (Cofactors covalent binding)
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Disulfide bond-cross links (Cys-Cys)
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Isopeptide (N-(γ-Gln)-Lys
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Transamidation (Gln→Lys or Ornithine-α-NH2)
(Transglutaminases)


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Blood clotting factor VIII – coagulation
Tissue Transglutaminase reaction
Cell proliferation, aging, endocytosis, secretion, differentiation,
apotosis, programmed cell death
C.
Covalent Cofactors
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Biotinyl lysine (Carboxylase, transcarboxylases)
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Cys-bound linear tetrapyrrole (phycobiliproteins lightharvesting system of photosynthetic microorganisms)
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FAD-linked His, Cys, or Tyr (DHase, Oxidase)
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FMN-linked Cys
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Heme-covalent bound (Cyt. C)
D.
Membrane Anchors

α-NH2 myristoyl

Cys- fattyacyl thioether
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Ser- palmitate or other fatty acids esters
Thr-

C-terminal glycophospholipids
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C-terminal Cys – prenylated group
Farnesyl C15, Geranylgeranyl C20
E. Signaling, Recognition and
Structural Amplification
F.
Protein Turnover (Protein
Degradation)

Spontaneous Oxidation: Cys, His, Tyr, Met

Ubiquitination: Lys
G. Others

Iodination: Tyr, (Thyroid hormones)

Sulfation or methylation; Tyr / secreted proteins
Types of Post-translational
Modification
A. Modification Involving Peptide
Bonds Cleavage (limited proteolysis)
1. Peptide Bonds Cleavage (limited proteolysis, specific and
well-regulated )
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Signal leader peptide removed by signal peptidase (both in
prokaryotes and eukaryotes)
Precursor protein → mature protein (Insulin)
Zymogen → active enzyme
Trypsinogen → Trypsin
Pepsinogen → Pepsin
Prohormone → Hormone
Polyprotein → neuropeptides (peptide hormone ) conversion
2. Peptide Bond Isomerization (Intramolecular)


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Ser → esters
Cys → thioesters
Asp or Asn → isoaspartate
Prolyl peptide cis-trans isomerization (prolyl isomerase
catalyzed)
3. Peptide Bond Formation, Transpeptidation

peptide bond splicing with peptide deletion and/or
permutation Plant lectin – Concanvalin A
B. Modifications Involving
Amino and Carboxyl Termini
1. The N terminus：H3N+—
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N-Formyl- (C1)
N-Acetyl- (C2)
N-Acyl- (C2, C4, C6,
C8, C10)
N-Lauroyl- (C12)
N-Myristoyl- (C14)
N-Tetradeca (mono and
di)enoyl- (C14：1；
C14：2)
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N-AminoacylN-α-KetoacylN-MethylN-Pyrrolidone
carboxylN-GlucuronylN-Glycosyl-
2. The C Terminus：
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Amide
O-(ADP-ribosyl)O-Methyl-(N-Ethanolamine-glycan-phosphoinositides)
-(Nα-TyT)
C. Modifications Involving Individual
Amino Acid (Side Chains)
1. Arginine：
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Nω-(ADP-ribosyl)Nω-MethylNω-DimethylNω-Nω’-Dimethyl-
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Ornithine
Citrulline
Nω-Phosphoryl-
2. Asparagine：
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N-GlycosylAspartate
N-Methyl-
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Nε-(β-Aspartyl)lysine
erythro-β-HydroxyN-(ADP-ribosyl)-
3. Aspartate：
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D-Asp (racemization)
β-Carboxyerythro-β-Hydroxy-
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β-MethylthioO-PhosphorylO-Methyl-
4. Cysteine：HS-CH2
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Cystine
S-γ-GlutamylS-(2-Histidyl)S-(3-Tyr)
S-(sn-1-Glyceryl)S-(sn-1-Diacylglyceryl)S-(sn-1-{2,3,-Di-O-[3’ ,7’ ,11’ .15’tetramethylhexadecyl]}glyceryl)S-PalmitoylS-FarnesylS-GeranylgeranylS-Heme
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S-Phycocyanobilin
S-p-Coumaroyl
S-(6-Flavin [FMN])
S-(8α-Flavin [FAD])
S-Coenzyme A
S-(ADP-ribosyl)S-GlycosylDehydroalanine
Lysinoalanine
Lanthionine
Selenocysteine
5. Glutamate：
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O-(ADP-ribosyl)
γ-CarboxyO-MethylNα-(γ-Glutamyl)-Glu1-5
Nα-(γ-Glutamyl)-Glu3-34
N- (γ-Glutamyl)ethanolaminephosphate)
S-γ-Glutamyl-Cys is listed under Cys
6. Glutamine：
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Glutamate
Nε-(γ-Glutamyl)lysine
N-(γ-Glutamyl)-L-ornithine
N-(γ-Glutamyl)polyamine
N,N-(Bis-γ-glutamyl)polyamine
N5-Methyl-
7. Histidine：
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Diphthamide
Nτ-(ADP-ribosyl)diphthamide
N-PhosphorylNπ-Methyl4-Iodo-and diiodoNτ- and Nπ –(8α-flavin [FAD])
Nπ-(8α-Flavin[FMN])
8. Lysine：
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Nε-AcetylNε-( Nα-Monomethylalanyl)Nε-Murein (peptidoglycan)
Nε-LipoylNε-BiotinylNε-UbiquitinylNε-PhosphorylNε-PhosphopyridoxylNε-Retinyl-
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Nε-GlycosylNε-Mono-, di- , trimethylHypusine：Nε-(4-amino-2-hydroxybutyl)Allysine
δ-Hydroxyδ-Hydroxyallysine
Cross-links
(desmosines, syndesines, pyridinolines)
δ-Glyxosyloxy-
9. Methionine：

Sulfoxide
10. Phenylalanine：
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β-Glycosyloxy-
11. Proline：
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3-Hydroxy4-Hydroxy3,4-DihydroxyO4-ArabinosylhydroxyO4-GalactosylhydroxyO4-Glucosylhydroxy-
12. Serine：HO-CH2
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Selenocysteine
O-PhosphorylO-PantetheinephosphorylO-(GlcNAc-1-phosphoryl)O-(Glycerol-1-phosphoryl)O-Methyl-
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O-GlycosylAlanino(τ- or π-histidine)
Lanthionine
O-AcetylO-Fatty acyl-
How modifications are made ?
A. Nonenzymatic Reaction
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deamidation：Asn, Gln
racemization：Asp, Ser
dehydroalanine：Cys, phosphor-Ser
slow oxidation：Cys, His, Met
slow cleavage and permutation of peptide bonds
reducing sugar reaction with NH2-group of aa’s or side
chains (Lys)：Maillard reaction (Browing reaction)；
Schiffs base reaction.
B. Enzymatic Reaction
1. Irrversible, Unidirectional Reaction (permanently modified)


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N-linked glycosylation
Carboxyl methylation
S-isoprenylation-Cys
2. Irrversible, Bi-directional Reaction. (Signal Amplificaion)
 Phosphorylation (protein kinase) / Dephosphorylation
(phosphatase)：Ser, Tyr, Thr.

Uridylyl and adenylyl transfer in bacterial glutamine
synthetase
3. Reversible Reaction

RS-SR + R’-SH ↹ R’-S-S-R + RSH(disulfide isomerase)
Coupled with protein-folding process