intracellular compartments and protein sorting 2 Flashcards
What is the signal Hypothesis
When a protein is inserted into or crosses the membrane via a membrane bound ribosome. It occur usally when a SRP recongized signal sequence on protein as its being transcribed. The SRP guides the ribosme- protein complex to membrane to finish its job.
How are the proteins imported into the mitochondrial matrix ( steps)?
- Precursor proteins are unfolded via chaperone proteins (cytosolic HSP 70)
- Import receptors on TOM bind to the Signal sequence of incoming protein
- Chaperone proteins are stripped and protein is feed into translocation channel
- sig seq first
- TOM transport protein into inner membrane space (across outer Mem)
- Protein binds to TIM 23 complex and moves through channel into matrix
- As it moves through TIM 23 once it enters the matrix it is bound to mitochondrial HSP70
- It keeps it unfolded until protein is translocated then ATP is hydrolzied and HSP70 is removed and HSP60 is used ( via another ATP to trigger correct folding)
- Signal sequence cleaved by Signal Peptidase
What is happening at each region ( A, B, C, D, E) in this photo
A. Nuclear encoded proteins binds to tom and then reaches TIM. TIM cleaves Signal sequence and inserts and folds protein into the inner mitochondrial membrane. the hydrophobic region of the protein in the inner membrane space
B. Mito. enconded protein is produced (Skips TOM and TIM) binds to OXA via a second signal sequence and is folded and inserted into inner membrane space. the hydrophobic region of the protein in the inner membrane space
C. Protease cleves the hydrophobic region from the embedded portion of the protein
D. reduced protein ( loaded with S-H) enters TOM complex. Recongized and Oxidized by MIA40 and causes formations of Disulfide bridges into the the imported protein
E. nuclear encoded protein enters through TOM meets intermembrane space chaperones and binds to TIM22 complex and then is inserted and folded into the inner membrane protein.
If a protein is signaled to imbedded into the outermitochondrial membrane when does it occur?
What part of translocation into the mitochondria requires Energy?
- Bound Cytosolic HSP 70 is dissasociated via ATP hydrolysis
- Transport through TIM 23 via Membrane potential and attached to mitochondiral HSP 70
- Mitochondrial HSP 70 bound to TIM 23 released on matrix side and release protein via ATP hydrolysis
- Mitochondiral HSP 60 helps folding of protein via ATP hydrolysis
How do proteins get past the inner membrane?
Translator (translocase) of the innder membranes
TIMs
Tim 23
- Transports soluble proteins into matrix and helps insert membrane proteins in inner membrane
Tim 22
- mediates insertion of a specfic class of proteins (ATP, ADP, and Pi transporter)
How are Mitochondrial signal sequences arranged, read, and processed ?
- They lie on the N terminal and internal signal sequences
- Postively charged residues clter on one end and uncharged hydrophobic on the other come to gether and form an amphiphillic alpha helix
- They are then read via there configuration (NOT SEQUENCE) by recepter proiens
- Protein translocaters mediate translocation
(fun fact: signal sequence for matrix proteins are best understood )
How is a protein translated across the ER?
-
SRP wraps around the large ribossmal subunit
- one end binds to ER signal equence
- another binds to elongation factor binding site
- protein synthesis is blocked allowing for protein to enter the ER membrane
- Interaction brings new complex to Translocator
- SRP and receptor released and proten is translocated across the ER membrane
What is the structure of the ER translocator
*
What is the signal recongition particle?
Varies in amino acid sequence
Has 8 or more non polar amino acids at center
guides protein to ER along with SRP recepter
made of 6 different poly peptides and small RNA molecules
Rod shaped w/ large hydrophobic pockets lined with mets
How is a protein integrated into ER membrane as a transmembrane protein?
- Initial process similiar to soluble proteins
- N terminal sequence initaties translocation
- integration of membrane proteins require that some portions of protein pass through and others dont
- addition hydropphobic region in polypeptide stops transfer process before entire polypeptide is translocated
- stop transfer signal
- Anchors protein in membrane after transfer signal has been cleaved and released
- lateral gating helps remvoe the cleaved start transfer peptide and to inegrate stop trans fer signal into bilayer
- In multiple TM proteins several combinations of start transfer and stop transfer determine topology of the protein
How does protein translocation across ER
- SRP binds to ER signal sequence and protein is directed toward ER
- Signal sequence triggers opening of translocator and SRP released. (I)
- Signal sequence interact w/ a specfic site within the pore (opens it too) (II)
- this called strart transfer signal
- Dual recognition = specficity ( i & II )
- interaction occurs b/w lipid portion of ER too
- Signal Peptidases cleaves off signal which escapes from lateral opening in the pore.
How do proteins get past the outer membrane of the mitochondria?
TOM COMPLEX
- Translocator of Outer membrane
- Required for IMPORT OF ALL NUCLEAR ENCODED PROTEINS
- INSERTS proteins into them in the outer membrane
How are proteins import INTO the outer Membrane of the Mitochondria?
Protien -> TOM complex -> inter membrane space -> binds to chaperone - > binds to SAM complex (outer mem) -> SAM inserts and folds into outer membrane
What are the 5 translocaters for inner and outer mitochondrial membranes?
TOM and TIM (2 componets)
- receptors for mitochondrial precursor proteins
- translocation channels
SAM complex (Sorting and Assembly Machinery)
- translocates and inserts/fold beta barrel proteins in the outer membrane
OXA complex
- Mediates insertion of proteins synthesized in mitochondria
