ADME Flashcards
2 pathways proteins are degraded in mammal cells
Lysosomal degradation
Proteasome degradation
protein degradation depends on
§ Structural protein = long (no need high turnover)
§ Regulatory protein = short (after respond to environment change, not needed)
protein degradation impt
§ Proper regulation of cell signalling pathways (maintain normal protein turnover)
§ To remove misfolded (not native conformation) and damaged (wear and tear) proteins that can lead to abnormal cellular activities
- Prevent no activity/ abnormal activity: DISEASED STATE in body
HIF-1 a
Transcription factor
□ For oxygen homeostasis during hypoxic conditions
□ Induce expression of genes involved in:
- ANGIOGENESIS
- Cell migration
- Glycolytic pathway
Gene VHL:
□ Code protein pVHL
□ Substrate-recognizing component of multimeric E3 ligase
○ Ubiquitin-proteasome system
○HIF1a (become substrate) for ubiquitination (degrade)
normal HIF-1a — normoxic condition
- HIF-1a maintained at low lvls (undetectable)
- Half-life 5-8min
- Hydroxylated (Pro402, Pro564)
- By oxygen-dependent propylhydroxylase
○ Targeted for ubiquitination - Ubiquited HIF1a degraded by 26S proteasome
normal HIF-1a — hypoxic condition
- HIF1a used to incr expression of target genes
○ Incr (MMP) matrix metalloproteinase
○ Incr vascular endothelial GF (VEGF)
- Incr invasion, metastasis, angiogenesis
Von Hippel-Lindau (VHL) disease pathophysiology
- Hereditary disease, autosomal dominant mutation in allele of gene VHL
1) Mutated pVHL lead to failure to degrade HIF1a
2) Accumulated
3) Incr HIF1a transcriptional activity
4) incr expression of target genes (MMP, VEGF)
Von Hippel-Lindau (VHL) disease effects
- predispose for tumour types
(pheochromocytomas, hemangioblastomas CNS, clear-cell renal carcinoma, retinal capillary angiomas) – high vascularisation
Cells act like they are at hypoxic condition, so incr blood vessel formation everywhere
- formation of tumours everywhere
Lysosomal degradation OCCURS AT
- Occur in lysosome
- Mem-bound organelles
- Acidic interior pH4.5
- 10-20% of proteins
lysosomal degradation _____ process
effect on what proteins?
- Non-specific process
- As long as in lysosome
- Mem associated proteins, alien proteins INTERNALISED (endocytosis – phagocytosis, pinocytosis, receptor-mediated endocytosis)
*Not intracellular proteins
Phagocytosis
a. Cell eating
b. Large solid particles
i. Cell debris, dead cells, protein aggregates, pathogenic microorganism (bact), dust, particulate non-living matter
c. Phagocytosed into PHAGOSOMES
Pinocytosis
a. Cell drinking of extracellular fluid
b. Fluid: solute dissolved, ingested by budding of small vesicles from cell mem
c. non-specific
Receptor-mediated endocytosis
a. Molecules taken up are LIGANDS recognised by receptors expressed on cell mem of cells
b. Specific molecules:
i. hormone, metabolites, proteins, some virus
c. Internalised into coated vesicles
d. Fuse with endosomes
e. Sent to lysosomes for degradation// RECYCLE to plasma mem
Proteasomal degradation effect is on ____
- 80-90% of intracellular proteins
- Degrade by 26S proteasome
- Specific process
- Ubiquitinated proteins
Some non-ubiquitinated
- Ubiquitinated proteins
proteasome size
- Large cylindrical particle
- At least 33 subunits
- ~2.5MDa
- Different variants exist in cells
BUT 26S proteasome is found in ALL CELLS
26s proteasome function
- Specific degradation of regulatory proteins
- Remove damaged proteins
26s proteasome structure
○ 20S core particle
- 4 heptameric rings
- 2 outer (a subunit)
- 2 inner (b subunit)
□ Inner ring house central cavity with proteolytic active sites
○ Cap: 19s regulatory particle (both ends)
20S core particle function
- Degradation chamber reached through channel running along LONG AXIS
1) NARROW Entrance: folded protein, partially unfolds to translocate into 20s core protein
2) Protein unfolds
a. Stretch along channel
b. Hydrolysed to short pepetides (3-25aa)
3) Released from opp end of channel
19s regulatory particle (lid, base) function
a. Has ATPase subunits
b. Substrate recognition
c. Unfolding
d.Translocation into the core
steps of degradation inside 26s proteasome
- Gate of 20s core particle closed
- Proteolysis is selective
- Polyubiquitin chain formed on protein (proteasome recognises chain)
1) Ubiquitin tag CLEAVED by deubiquitinating enzymes (DUBs)
a. Into monomers
2) Monomers escape from proteasomes
a. Recycled to label other protein substrates
3) Proteasome engage protein substrate
a. Pp unfolds, translocate into core for degradation
b. Narrow core – regulate entry
4) 19s cap hydrolyse ATP to provide energy, drive:
a. removal of Ub
b. Protein unfolding
c. Transfer of unfolded protein to inner chamber of proteasome
i.Released as short peptide fragment (other end 19s)
Delivery to proteasome
Substrate bring to proteasome
a) Interact with 19s regulatory particle subunit
b) By adaptor protein
- Bind both proteasome & polyubiquitination chain
- Deliver for degradation
c) Some degraded w/o ubiquinated
Ubiquitin (Ub)
○ 76 residue pp
-Contain 7 lysine (6,11,27,29,33,48,63)
○ Attaches to substrate protein through
-Isopeptide bond
- c-terminal Gly of ub + amino grp Lys in substrate
○ Minimal 4 Ub monomers linked through Lys 48 to be functional
Monoubiquitination
○ Attach 1 Ub protein
○ Predominant regulatory modification (post-translational mod)
monoubi of histones & TF
□ Incr transcription
monoUb of surface cell receptors
□ Signal for endocytosis
□ Degradation in lysosome
Traditional chemical based drugs
<1000Da
Chemically synthesized, purified to homogeneity
Chemical modification lead to drastic changes in activity. New drugs for new uses
MAY have off target effects
Biologics/ biopharm drugs characteristics
* Recombinant proteins * MAB (monoclonal Ab) * Nucleic acid-based products Also have clinical devices, diagnostics
Large, kDa
Derived from living source
(human, animal tissue, cells, microorg)
Not easily characterized
Not easily refined
Called by same name despite modification in 1/ more aa residues
More predictable, less SE
Targeted therapy/ personalised (since disease are affected by the proteins it is made from)
Other than immunogenicity
Challenges of biopharmaceuticals:
immunogenicity
degradation
distribution of macromolecule –> tissue
Immunogenicity
a. Contaminants of whole cells, CHO cell, bact cells
b. Poor purification
c. Excipients (solvent)
Lead to rash, anaphylaxis etc
Degradation
a. Protease degradation in biological fluids (ECF) upon admin
i. When MW > 200 kDa: phagocytosis involved
b. Degraded intracellularly
i. Lysosomal
ii. Intracellular proteases
iii. Ubiquitin-proteasomal degradation
Distribution of MACROMOLE —> tissue
limited by permeability (Porosity of vasculatures)
MAB KDa size
2 light chain (25kDa each), 2 heavy chain (55 kDa each) = 160 kDa
Compare to insulin 5-6kDa
IL, GF, cytokines 5-10kDa