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Questions and Answers
What is the default location of proteins without address labels?
What is the default location of proteins without address labels?
What is the function of nuclear localization signals (NLS) in proteins?
What is the function of nuclear localization signals (NLS) in proteins?
What is the characteristic of the sequence that allows proteins to be targeted to peroxisomes?
What is the characteristic of the sequence that allows proteins to be targeted to peroxisomes?
Where are proteins destined for the Endoplasmic Reticulum usually dispatched?
Where are proteins destined for the Endoplasmic Reticulum usually dispatched?
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What is the characteristic of protein targeting to mitochondria and peroxisomes?
What is the characteristic of protein targeting to mitochondria and peroxisomes?
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What is the function of the protein importin in nuclear protein targeting?
What is the function of the protein importin in nuclear protein targeting?
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Study Notes
Protein Synthesis and Targeting
- Proteins are initially synthesized on cytosolic ribosomes and may be dispatched to different destinations based on address labels within their primary sequence.
- Proteins without address labels remain in the cytosol by default.
Nuclear Localization
- Nuclear localization signals (NLS) enable fully folded proteins to move reversibly to the nucleoplasm via nuclear pores.
- NLS is a stretch of 6-8 positive residues anywhere in the primary sequence, recognized by the protein importin.
- Nuclear translocation is regulated by unmasking a NLS for many proteins.
Mitochondrial Targeting
- Proteins destined for mitochondria are fully translated and later modified.
- There are four destinations for proteins in the mitochondria: inner membrane, outer membrane, inter-membrane space, and matrix.
- For matrix proteins, an N-terminal amphipathic helix is recognized by a chaperone protein.
Peroxisomal Targeting
- Proteins destined for peroxisomes have a C-terminal SKL-e sequence, recognized by a PTS1 receptor.
- This targeting mechanism is non-functional in Zellweger syndrome.
General Targeting Principles
- All proteins must cross a membrane, requiring partial unfolding to be threaded through a protein pore within the target membrane.
- Targeting to peroxisomes and mitochondria is irreversible, whereas nuclear translocation is reversible.
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Description
This quiz covers the process of protein synthesis and transport, including the role of address labels and nuclear localisation signals in protein targeting and the importance of protein folding in membrane transport.
