Download Biosynthesis and degradation of proteins

Biosynthesis and degradation of
proteins
Bruno Sopko
Content
• Proteosynthesis
• Post-translation processing of proteins
• Protein degradation
Proteosynthesis
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Aminoacyl-tRNA formation
Iniciation
Elongation
Termination
Aminoacyl-tRNA formation
Amino acid + ATP ↔ Aminoacyl-AMP + PPi
Aminoacyl-AMP + tRNA ↔ Aminoacyl-tRNA + AMP
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Each amino acid has „its own“ tRNA and aminoacyl-tRNA
synthetase (ARS)
Reactions are cytosolic
Errors are corrected by specific correcting enzymes
ARS have other enzyme activity (other signaling molecule?)
Other ARS functions
Proteosynthesis Iniciation
Elongation
Termination
Post-translation processing of proteins
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Secondary structure and role of the chaperons
Proteolytic modifications
Glycosylation
Other modifications (hydroxylation,
phosphorylation, acetylation, methylation,
carboxylation)
Protein transfer after translation
Contranslational translocation
Contranslational translocation –transmembrane proteins
Transmembrane proteins - examples
• Type I – glycophorin, LDL receptor, influenza HA
protein, insulin receptor, growth hormone
receptor …
• Type II – transferrin receptor, influenza HN
protein, Golgi sialyltransferase, Golgi
galactosyltranferase …
• Type III – cytochrome P450 …
• Type IV – G-protein, glucose receptors (GLUT 1
…), connexin, voltage gated Ca2+ channel …
Secondary structure
Secondary structure –HSP70 chaperon cycle
Secondary structure – GroEL/GroES system
Secondary structure – overview
Protein disulfid isomerase (PDI) and peptidyl prolyl cis-izomerase
PPI:
Proteolytic modification - insulin
N-Glycosylation
Other modifications
• O-glycosylation
• Hydroxylation (hydroxyproline, hydroxylysine)
• Methylation (mono- , di- and even
trimethyllysine)
• PHOSPHORYLATION
• Carboxylation (γ-carboxyglutamate, vitamin K,
fibrinogen)
• Acetylation
• ……..
Protein degradation
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Proteases
Protein degradation systems
Ubiquitin and proteasome
Activation of proteases
Protease inhibitors
Proteases
• Serine proteases (trypsin, chymotrypsin,
elastase ….)
• Aspartate proteases (pepsin, some proteases
found in lysosomes, renin, HIV-protease …)
• Metalloproteases (carboxypeptidases, various
matrix metalloproteases …)
• Cysteine proteases (papain, cathepsins,
caspases, calpains …)
Protein degradation systems
• Vacuolar (lysosomes, endosomes, ER, …)
• Ubiquitin pathway (proteasome)
Ubiquitin pathway
Activation of proteases
• Most proteases are synthesized as larger pre-proteins.
During activation, the pre-protein is cleaved to remove an
inhibitory segment.
• In some cases activation involves dissociation of an
inhibitory protein
• Activation may occur after a protease is delivered to a
particular compartment within a cell or to the extracellular
milieu.
• Caspases involved in initiation of apoptosis are activated by
interaction with large complexes of scaffolding and
activating proteins called apoptosomes.
Protease inhibitors
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IAPs are proteins that block apoptosis by binding to and inhibiting caspases. The
apoptosis-stimulating protein Smac antagonizes the effect of IAPs on caspases.
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TIMPs are inhibitors of metalloproteases that are secreted by cells. A domain of
the inhibitor protein interacts with the catalytic Zn2+.
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Cystatins are inhibitors of lysosomal cathepsins. Some of these (also called stefins)
are found in the cytosol and others in the extracellular space. Cystatins protect
cells against cathepsins that may escape from lysosomes.
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Serpins are widely distributed proteins that utilize a unique suicide mechanism to
inhibit serine or cysteine proteases.
A large conformational change in the serpin accompanies cleavage of its substrate
loop. This leads to disordering of the protease active site, preventing completion
of the reaction. The serpin remains covalently linked to the protease as an acylenzyme intermediate.
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Non-specific: α2-macroglobulin
Fate of the protein
Literature
• Marks´ Basic Medical Biochemistry, A Clinical
Approach, third edition, 2009 (M. Lieberman,
A.D. Marks)
• B. Wilkinson, H.F. Gilbert / Biochimica et
Biophysica Acta 1699 (2004) 35–44
• F. Ulrich Hartl, Andreas Bracher & Manajit HayerHartl, Molecular chaperones in protein folding and
proteostasis, Nature 475 (2011)