Question

Mutation Cremoves the signal sequence from prolon 3 Mutation D prevents the fusion of all vesicles to the cell membrane 2. You are studying a transmembrane cell surface protein called Hip in yeast cells. You generate a wild-type Hip-GFP fusion protein and 2 mutant proteins as shown below: M Wild-type protein-GFP Hip GFP Stretch of 6 hydrophobic amino acids Stretch of 18 hydrophobic amino GFP Mutant 1-GFP N- Mutant 2-GFP N- You examine yeast cells expressing the above proteins separately, and look for GFP fluorescence and localization of these proteins. The results are as shown below: Protein Wild-type Hip-GFP Localization of fluorescence ER membrane, vesicles, Golgi and cell membrane Cytosol Mutant 1-GFP Mutant 2-GFP ER lumen a. Why is wild-type Hip-GFP found in several cell organelles?

Answer 1

First of all let's compare the three different proteins.

The wild type one is the actual functioning protein while the mutants lack certain stretches of amino acids.

Since the wild type have the whole sequence intact it is being able to be transported through different organelles.

Comparison of wild type with mutant-1

As you can see in the picture, Mutant one lack the stretch of 6 hydrophobic amino acids on the N-terminal.

When mutant is localised with the help of fluorescence, it is found in the cytosol.

When we compare this with mutant-2, mutant-2 can be found in the ER. Mutant-2 have the stretch of those 6 hydrophobic amino acids which mutant-1 doesn't have Thus we can conclude that these 6 amino acids are necessary for the protein's transport from cytosol to ER lumen.

Comparison of Mutant-2 with wild type:-

Mutant can be localised inside the ER. We have already established why Mutant-2 can be transported to ER. When we compare it with wild type, we can see that it doesn't have the middle section of 18 hydrophobic amino acids. So these amino acids play a role in the further transport of the protein.

Proteins are transported inside the cell in this order

Cytosol to ER. Then from ER to vesicles, then these vesicles takes the proteins to Golgi complex and then from there it is taken to cell membrane.

From the above data, we come to this conclusion :-

Wild type can be found in several cell organelles because it have the sequences which are necessary and required for its proper transportation inside this cell, while mutants lack these and are unable to be sorted properly.

Thank you.