Question

What types of signal sequence(s) would you expect to find on each of the following types of proteins:

1. Na+/K+ Pump
2. DNA Polymerase
3. Mitochondrial chaperone protein
4. Flippases
5. A lysosome localized protease

  

Answer 1

• Na+/K+ Pump: This will be targetted to the plasma membrane of the cell. This is mediated by Signal Recognition Particle (SRP) that binds to transmembrane signal sequences, which are found in both, the alpha and beta subunits of the Sodium/Potassium pump.
• DNA Polymerase: The DNA polymerase would contain an NLS with the sequence K-R/K-X-R/K at the N terminus of the molecule.
• Mitochondrial chaperone protein: The mitochondrial matrix signal sequence is: N-MLSLRQSIRFFKPATRTLCSSRYLL. A chaperone protein that is present in the mitochondria will help fold the peptide in the correct orientation.
• Flippases: Flippases would also have an internal targeting sequence recognized by SRP and folded into the ER membrane prior to export to the plasma membrane.
• A lysosome localized protease: Lysosomal targetting is achieved by either incorporating