Protein Activity Control - ULisboabmg.fc.ul.pt/Disciplinas/FundBiolMolec/17ProteinActivity.pdf ·...
Transcript of Protein Activity Control - ULisboabmg.fc.ul.pt/Disciplinas/FundBiolMolec/17ProteinActivity.pdf ·...
Protein ActivityControl
Functional Proteins
Active vs inactive proteins
Steps in the creation of a functional protein
Cell 6.79
More than 100 different types ofcovalent modifications are known
Some ways in which the activity of gene regulatory proteins is regulated in eucaryotic cells
Each of these mechanisms is typically controlled by extracellular signals which are communicatedacross the plasma membrane to the gene regulatory proteins in the cell- SIGNAL TRANSDUCTION
Mechanisms are readily reversibleand therefore also provide the means to selectively inactivate gene regulatory proteins
Schematic representation of the four types of post-translational processing events
Genomes 11.23
Protein Folding
The aminoacid sequence contains all the information needed to fold the polypeptide
into its correct tertiary structure
The cellular mechanisms that monitor protein qualityafter protein synthesis
Cell 6.85
ex. amiloid
How a protein folds into a compact conformation
Cell 3.6
The co-translational folding of a protein
Cell 6.81
Molecular chaperones of Escherichia coli
Genomes 11.26
Structure of GroEL/GroES chaperonin(Hsp60)
Hsp70 chaperones bind to hydrophobic regionsin unfolded polypeptides, including those that are stillbeing translated, and hold protein in an open conformationuntil it is ready to be folded
Hps70 (dnaK)Hps40 (dnaJ)GrpE
Chaperone-and chaperonin- mediated protein folding
Lodish 3.11
Chaperons
• Ligam-se às proteínas em estádios precoces da sua síntese
• Impedem enrolamentos não produtivos
• Permitem que a proteína se enrole na forma termodinamicamente mais estável (estado de menor energia)
• A sequência de aminoácidos do polipéptido é que determina a estrutura final
Protein processing
Proteolytic CleavageChemical Modification
Intein splicing
Protein processing by proteolytic cleavage
Genomes 11.27
Ex. proteolytic cleavage : the pro-opiomelanocortinpolyprotein
Genomes 11.29
Ex. proteolytic cleavage: melitin and insulin
Genomes 11.28
Promelittin Melitin
24 aa
22 aa
Extracellular protease
Signal peptide- hydrophobic aa sequence thatattachs preproinsulin to the membrane, beforeexporting the protein through the membrane tothe extracellular environment
Ex. of protein processing by proteolytic cleavage
• Botulism (from the latim botulus “sausage”)- is a rare but serious paralytic illness caused by the botulinum neurotoxin (BoNT) produced by Clostridium botulinum.
• This disease is characterized by descending flaccid paralysis as a result of inhibition of acetylcholine release at the neuromuscular junction (BoNT belongs to the group of zinc-metalloproteases)
• It is synthesized as a single-chain polypeptide of approx. 150 kDa, subsequently cleaved to form a di-chain molecules, in which a single disulfide bond links the light (50 kDa) and heavy chains (100 kDa)
Chemical Modification
Primary and secondary levels of gene regulation
Genomes 9.22
Regulation the amount ofprotein that is beingsynthesized or changethe nature of the proteinin some way, for exampleby chemical modification
Common protein chemical modifications(after protein synthesis)
In red:Various chemicalgroups added to theaa side chains
Ex. of post-translational chemical modification ofcalf histone H3
Genomes 11.30
Modification Amino acids that are modified
Examples of proteins
Addition of small chemical groups
Acetylation (CH3CooH) Lysine Histones
Methylation (CH3) Lysine Histones
Phosphorylation (P) Serine, threonine, tyrosine Some proteins involved in signal transduction
Hydroxylation (OH) Proline, lysine Collagen
N-formylation (COH) N-terminal glycine Melittin
Addition of sugar side chains
O-linked glycosylation (hydroxil groups) Serine, threonine Many membrane proteins and secreted proteins
N-linked glycosylation (amino group) Asparagine Many membrane proteins and secreted proteins
Addition of lipid side chains
Acylation Serine, threonine, cysteine Many membrane proteins
N-myristoylation (miristic acid) N-terminal glycine Some protein kinases involved in signal transduction
Addition of biotin
Biotinylation Lysine Various carboxylase enzymes
150 different aa already described
Protein Degradation
Cell 6.82
Protein degradation... when?
Relation between N-terminal amino acid and half-life of E. coliβ-galactosidase proteins with modified N-terminal amino acids
N-terminal Amino Acid Half-life
Met, Ser, Ala, Thr, Val, Gly
Ile, Glu
Tyr, Gln
Pro
Phe, Leu, Asp, Lys
Arg
PestProGlnSerThr
Half-life less then 2 hours
more than 20 h
30 min
10 min
7 min
3 min
2 min
Acerca da degradação de proteínas
• Várias vias de degradação – Lisossomas: contêm uma série de hidrolases e enzimas
proteolíticos, degradando essencialmente proteínas transmembranares e do lúmen dos organitos
– Proteossoma: complexo multiproteico que degrada proteínas ubiquitinadas, localizadas sobretudo no núcleo e no citosol.
Ex. Factores de transcrição, proteínas da regulação do ciclo celular como as cinases e fosfatases etc.
• Processos altamente selectivos e rápidos
• Eucariotas- descrito o Proteossoma
Lodish 3.13
Ubiquitin and the marking of protein withmultiubiquitin chains
Ubiquitin-mediatedproteolytic pathway
(7-8 residues)
The export and degradation of misfolded ER proteins
Cell 12.55
Protein Sorting
A simplified “roadmap” of proteintraffic
Cell 12.6
Through nuclear pores
Through translocator proteins
Through vesicules
Vesicle budding and fusion duringvesicular transport
Cell 12.7
Lodish 17.3
Overview of the secretoryand endocytic pathwaysof protein sorting
Lodish 17.1
Overview of major protein-sorting pathways in eukaryotic cells
Citosol
Non-secretory pathway
Free and membranes-bound ribosomes
Cell 12.37
Two ways in which a sorting signal (orsignal sequence) can be built into a protein
Cell 12.8
Some Typical Signal sequences
Hidrophylic aa
Hidrophylic aa/ hydrophobic aa
Target Organelle Usual Signal Location within Protein
Signal Removal* Nature of Signal
Endoplasmic reticulum N-terminal (+) "Core" of 6 - 12 mostly hydrophobic amino acids, often preceded by one or more basic amino acids
Mitochondrion N-terminal (+) 20 to 50 nonconsecutive Arg or Lys residues, often with Ser and Thr; no Gluor Asp residues
Chloroplast N-terminal (+) No common sequence motifs; generally rich in Ser, Thr, and small hydrophobic amino acid residues and poor in Gluand Asp residues
Peroxisome(matrix)
C-terminal (most proteins)N-terminal (few proteins)
( ) Usually Ser-Lys-Leu at extreme C-terminus
Nucleus Internal ( ) One cluster of 5 basic amino acids, or two smaller clusters of basic residues separated
Uptake-targeting Sequences that direct Proteins from the Cytosol to Organelles
The signal hypothesis
Cell 12.40
How ER signal sequences and SRP directribosomes to the ER membrane
Cell 12.42SRP- signal-recognition particle (citosol ribonucleoprotein)
Three ways in which protein translocation can bedriven trough structurally similar translocators
Cell 12.45
A model for how a soluble protein istranslocated across the ER membrane
Cell 12.46
Integration of a single-pass membrane proteinwith an internal sequence into the ER membrane
Cell 12.48
Integration of a double-pass membrane proteinwith an internal signal sequence into the ER membrane
Cell 12.49
Lodish 17.21
Lodish 17.25
Lodish 17.16
Cell 12.57
Steps at which eukaryotic gene expression can be controlled
Cell 7.5
Protein denaturation agents
Denaturation and spontaneous renaturationof a small protein
Genomes 11.24
The structure and function of the Hsp60 family of molecular chaperones
Cell 6.84
Intein splicing
Intein splicing- self-splicing of proteins
-150 conserved aa peptide
- cut, generally occurs downstream a Ser,Thr or Cys aa
- present in bacteria, Archae and eucaryotes
A polypeptide might have several inteins
Some of them after excision, are proteins themselves