Peroxisome Protein Targeting: L13

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Questions and Answers

What role do peroxisomes primarily play in cellular processes?

Protein synthesis

Energy production through ATP synthesis

Redox homeostasis and lipid metabolism (correct)

DNA replication

Which of the following statements about protein import into peroxisomes is correct?

All proteins are imported into peroxisomes without modification.

Proteins are imported via vesicular transport.

Import is only selective for lipid-based proteins.

Proteins require specific targeting signals for import. (correct)

What is a characteristic of peroxisomal protein translocation?

It occurs only after proteins are fully folded.

It uses the same machinery as mitochondrial import.

It can occur post-translationally. (correct)

It involves co-translational translocation.

Which of the following statements accurately describes the importance of peroxisomes in eukaryotic cells?

They synthesize a variety of essential lipids. Signup and view all the answers

What might be a consequence of peroxisome biogenesis disorders?

Disruption in lipid metabolism and homeostasis Signup and view all the answers

What role do YG repeats in PEX13 play in peroxisomal import?

They promote diffusion of PEX5-Cargo complexes. Signup and view all the answers

How does the PEX5 receptor return to the cytoplasm after cargo dissociation?

In an unfolded state Signup and view all the answers

What is a characteristic of peroxisomal import according to the information provided?

It involves large protein complexes being imported. Signup and view all the answers

Which statement about PEX5 is accurate?

PEX5 binds to cargo with a peroxisomal targeting signal (PTS). Signup and view all the answers

What structure facilitates the import of PEX5-cargo complexes into peroxisomes?

A mesh-like structure created by YG repeats. Signup and view all the answers

What is the main function of peroxisomes in relation to electrons?

They catalyze reactions that produce peroxide. Signup and view all the answers

Which receptor is primarily responsible for recognizing PTS1?

PEX5 Signup and view all the answers

What complex interacts with PTS2 during the peroxisomal import process?

PEX5 complex Signup and view all the answers

Which amino acids are part of the N-terminal sequence for PTS2?

[RK]-[LVIQ]-X-X-[LVIHQ] Signup and view all the answers

What is a unique feature regarding the capacity of peroxisomes?

They are capable of importing large folded proteins. Signup and view all the answers

What is the role of PEX13 and PEX14 in peroxisomes?

They form a translocation complex for importing cargo. Signup and view all the answers

What structural feature is present in PEX5 that allows it to interact with PTS1?

Tetratricopeptide repeats (TPRs) Signup and view all the answers

How do proteins commonly enter peroxisomes?

By interacting with other peroxisomal cargoes Signup and view all the answers

What is the role of PEX5 in peroxisomal import?

To guide proteins to the peroxisomes Signup and view all the answers

Which peroxisomal cargo interacts with Malate dehydrogenase (Mdh2) for entry into peroxisomes?

Mdh3 Signup and view all the answers

What is the primary function of PEX13 and PEX14 in the import mechanism?

To transport the PEX5-cargo complex inside peroxisomes Signup and view all the answers

Which statement about the Peroxisome Targeting Sequence (PTS) is true?

PTS-containing proteins are recognized by PEX5 Signup and view all the answers

What does the process of protein import into peroxisomes resemble?

Nuclear pore transport Signup and view all the answers

Which of these components is not part of the peroxisomal import mechanism?

Cytoplasmic chaperones Signup and view all the answers

What is a key characteristic of the piggybacking mechanism?

Cargo proteins can utilize other proteins for entry into peroxisomes Signup and view all the answers

What role does ATP play in PEX5 recycling?

It is necessary for the ATPase activity of PEX1/PEX6. Signup and view all the answers

What happens with the loss of PEX5 in cells?

Impaired import leading to Peroxisome Biogenesis Disorder occurs. Signup and view all the answers

What are the neurological defects associated with the Zellweger spectrum of PBD?

Demyelination. Signup and view all the answers

Which targeting signals allow proteins to localize to multiple cellular compartments?

Multiple targeting signals, including PTS and MLS. Signup and view all the answers

What is the state of protein during the post-translational targeting pathway through PEX5?

Fully folded. Signup and view all the answers

How does the presence of both PTS and MLS affect protein localization?

Proteins can localize to different compartments. Signup and view all the answers

Is it possible for a protein without a targeting sequence to be imported into cellular compartments?

No, it requires specific targeting signals. Signup and view all the answers

What receptor is involved in the import of proteins with a C-terminal PTS1?

PEX5. Signup and view all the answers

Study Notes

Protein Targeting to Peroxisomes

Peroxisomes are organelles involved in redox homeostasis and lipid metabolism.
Proteins are targeted to peroxisomes via specific signals.
Two main types of targeting signals exist: PTS1 (peroxisomal targeting signal 1) and PTS2 (peroxisomal targeting signal 2).
PTS1 is a C-terminal tripeptide sequence that directs proteins into peroxisomes. A typical PTS1 sequence is [SAGCN]1-[RKH]2-[LIVMAF]3.
PTS2 is an N-terminal amino acid sequence typically described as RK-[LVIQ]-X-X-[LVIHQ]-[LSGAK]-X-[QH]-[LAF].
PEX5 is the receptor for both PTS1 and PTS2 signals, and it interacts with the PTS signals via tetratricopeptide repeats (TPRs).
PEX13 and PEX14 form a translocation complex that helps import cargo into peroxisomes.
PEX5-Cargo complex binds to the PEX13/14 translocation complex to transport cargo into the peroxisomal lumen.
Importing the cargo into the peroxisomes does not require energy.
PEX5 recycling to the cytosol requires energy. ATPase is involved in PEX1/PEX6.
Proteins can enter peroxisomes through interaction with other peroxisomal cargoes, a process called "piggybacking".
Proteins without a targeting sequence can still enter into peroxisomes via other proteins that already have targeting sequences.

Peroxisome Targeting Sequence (PTS)

PTS1 targets cargo proteins to the peroxisome, typically at the C-terminus of a protein.
PTS2 targets proteins to the peroxisome at the N-terminus.
These targeting sequences are recognised by PEX5.
Proteins targeted with a PTS do not need energy to enter the peroxisome.

Peroxisome Biogenesis Disorders (PBDs)

Loss of PEX5 leads to impaired peroxisomal import and loss of peroxisomal functions.
These disorders are characterized by neurological issues, including demyelination.
They are known as autosomal recessive disorders.

Protein Import Without PTS

Proteins can be imported into peroxisomes without a PTS if they interact with other cargo proteins possessing PTS.
For example, Mdh2 enters the peroxisome by interacting with Mdh3 protein which contains PTS1.

PEX Proteins

PEX5: receptor for PTS signals.
PEX13 and PEX14: translocation complex; aid in cargo import.

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Description

Test your knowledge on the role of peroxisomes in cellular processes, their protein import mechanisms, and implications of biogenesis disorders. This quiz covers crucial concepts related to peroxisomal functions and receptor interactions in eukaryotic cells.