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24 Cards in this Set
- Front
- Back
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Protein modification information
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- Residue= group being modified
- Enzyme= enzyme that catalyzes modification/ addition - Donor= where group comes from that gets added onto protein - Reversible or irreversible modification - Role of modification - Interesting notes - Type of modification |
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Disulfide Bonds
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1. Residues: side chain -SH of 2 Cys
2. Enzyme: disulfide isomerase (in ER) (enzymes secreted out of cell) 3. e- Acceptor: glutathione (GS-SG→2GSH) 4. Reversible: disulfide isomerase, thioredoxin - Role: extracellular protein stability (e.g., insulin, antibodies, collagen, hair, nails, etc.) - Intramolecular disulfide tethers two portions of a single polypetide chain; intermolecular tethers two separate polypeptide chains - oxidation reaction between S's of two Cys - primary structural arrangement |
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Proteolytic Cleavage
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1. Residues: many residue recognition sequences
2. Enzyme: proteases (many types); cleave inactive protein releasing a portion that then folds into active form 3. Donor: peptide bond hydrolyzed by H2O 4. Irreversible - Role: protein maturation, enzyme activation - majority of proteases in blood clotting - primary structural arrangement |
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Phosphorylation
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1. Residues: side chain -OH of Ser, Thr, Tyr
2. Enzyme: kinases 3. Donor: ATP→ADP (transfers terminal phosphate) 4. Reversible: phosphatases - alter conformation, specify recognition - highest occurring PTM (post translational modification), occurs in majority of intracellular proteins→ activates inactive proteins - localized electrostatic change (neutral→ negative) |
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Sulfation
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1. Residues: side chain -OH of Tyr
2. Enzyme: tyrosyl protein sulfotransferases 3. Donor: PAPS →PAP 4. Irreversible - Role: specify recognition - majority secreted; occurs primarily extracellular proteins (matrix; joint fluids) - localized electrostatic change (neutral→ negative) |
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Acetylation
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1. Residues: -NH3+ of N-term and Lys side chain
2. Enzyme: acetyltransferases 3. Donor: acetyl-CoA→CoA 4. Reversible: deacetylases - Role: alter conformation, specify recognition - 2nd highest PTM, majority intracellular - localized electrostatic change (positive→ neutral) |
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Methylation
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1. Residues: -NH3+ of Lys and Arg side chains
2. Enzyme: methyltransferases 3. Donor: SAM→homo-Cys 4. Reversible: demethylases - alter conformation, specify recognition - regulates majority histones for gene regulation along with acetylation - localized electrostatic change (positive→ neutral)) |
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Myristoylation
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1. Residues: -NH3+ of N-terminus
2. Enzyme: myristoyltransferase 3. Donor: myristoyl-CoA , CH3(CH2)12CO2- 4. Irreversible - membrane localization - majority N-term Gly, but others - lipid attachement; amide linkage |
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Palmitoylation
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1. Residues: side chain -SH of Cys
2. Enzyme: palmitoyltransferases 3. Donor: palmitoyl-CoA , CH3(CH2)14CO2- 4. Reversible: thioesterases - Role: membrane trafficking - significant role in synaptic plasticity - lipid attachement; thioester linkage |
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Farnesylation
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1. Residues: side chain -SH of Cys near C-term
2. Enzyme: farnesyltransferases 3. Donor: farnesylpyrophosphate (Fpp) 4. Irreversible - Role: membrane localization, protein recognition - 15 carbons (3 units of 5) - lipid attachement; thioester linkage |
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Geranylgeranylation
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1. Residues: side chain -SH of Cys near C-term
2. Enzyme: geranylgeranyltransferases 3. Donor: geranylgeranylpyrophosphate (GGpp) 4. Irreversible - Role: membrane localization, protein recognition - 20 carbons (4 units of 5) - lipid attachement; thioester linkage |
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N-linked Glycosylation
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1. Residue: side chain -NH2 of Asn (NxS/T)
2. Enzyme: glycosyltransferase 3. Donor: dolichol-oligosaccharide 4. Irreversible - cell adhesion, connective tissue - occurs in lumen of ER - glycosylation; N-glycoside linkage |
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O-linked Glycosylation
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1. Side Chain: side chain -OH of Ser, Thr
2. Enzyme: glycosyltransferase 3. Donor: UDP-saccharide 4. Irreversible - Role: mucins-lubricate/protect epithelial surfaces - synthesis in Golgi - glycosylation; O-glycoside linkage |
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Tyrosine
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1. Side Chain: side chain -OH of Tyr
2. Enzyme: glycogenin 3. Donor: UDP-glucose 4. (Ir)reversible ? - Role: primer for glycogen synthesis - only one known instance (protein that starts synthesis of starch) - glycosylation |
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Hydroxyproline (Hyp)
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1. Side Chain: side chain Cδ-OH of Hyp
2. Enzyme: glycosyltransferase 3. Donor: UDP-galactose or -arabinose 4. Irreversible - Role: extracellular matrix stability - occurs only in plants - glycosylation |
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Hydroxylysine (Hyl)
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1. Side Chain: side chain Cδ-OH of Hyl
2. Enzyme: glycosyltransferase 3. Donor: UDP-glucose, then -galactose 4. Irreversible - Role: unknown, fibril organization? - occurs in ER and only in animals - glycosylation |
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Proline Hydroxylation
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1. Side Chain: (R)Cγ
2. Enzyme: prolyl hydroxylase 3. Donor: O2 , α-ketoglutarate, Fe, ascorbic acid 4. Irreversible - Role: H-bonding in collagen - vitamin C deficiency→scurvy (collagen instability; British sailors ate limes) |
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Lysine Hydroxylation
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1. Side Chain: (R)Cδ
2. Enzyme: lysyl hydroxylase 3. Donor: O2 , α-ketoglutarate , Fe, ascorbic acid 4. Irreversible - Role: H-bonding in collagen, prime glycosylation - linked to Ehlers-Danlos syndrome (hypermobile joints, hyper elastic skin) |
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ADP-Ribosylation
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1. N-Linked Side Chains: His, Arg, Asn, Lys
O-Linked Side Chains: C-term of Lys 2. Enzyme: ADP-ribosyltransferases 3. Donor: NAD+ 4. Reversible: - Role: protein conformation, enzyme regulation |
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Ubiquitination
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1. Residues: -NH3+ of Lys
2. Enzyme: E1, E2, and E3 ubiquitin ligases 3. Donor: E1→ E2→ E3→target protein 4. Reversible: deubiquitinases - Role: alter conformation, specify recognition - targets proteins for transport and degradation |
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Histone Acetylation
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1. Residues: -NH3+ of Lys
2. Enzyme: histone acetyltransferases (HATs) 3. Donor: acetyl-CoA(CoA) →histones 2A,2B,3,4 4. Reversible: histone deacetylases (HDACs) - POSITIVE → NEUTRAL: reduce affinity that histone has for DNA by reducing attraction of positive Lys side chains to negative phosphate backbones= loosen DNA |
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Histone Methylation
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1. Residues: -NH3+ of Lys and Arg
2. Enzyme: histone methyltransferases (HMTs) 3. Donor: SAM(homo-Cys) →histones 3,4 4. Reversible: histone demethylases - POSITIVE → NEUTRAL |
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Histone Phosphorylation
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1. Residues: side chain -OH of Ser, Thr, Tyr
2. Enzyme: kinases 3. Donor: ATP(ADP) →histones 2B,3,4 4. Reversible: phosphatases - NEUTRAL → NEGATIVE |
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Histone Ubiquitination
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1. Residues: -NH3+ of Lys
2. Enzyme: E1, E2, and E3 ubiquitin ligases 3. Donor: E1→ E2→ E3→histones 2A,2B 4. Reversible: deubiquitinases -NEUTRAL → NEGATIVE |
