Question

You have two purified samples of protein Y: the wild-type (nonmutated) protein and a mutant version with a single amino acid substitution. When washed through the same gel-filtration column, mutant protein Y runs through the column more slowly than the normal protein. Which of the following changes in the mutant protein is most likely to explain this result?

1) the loss of a binding site on the mutant protein surface through which protein Y normally forms dimers
2) a change that results in the mutant protein's acquiring an overall positive instead of a negative charge
3) a change that results in the mutant protein's being larger than the wild-type protein
4) a change that results in the mutant protein's having a slightly different shape from the wild-type protein
5) a change that results in the mutant protein's acquiring an overall negative instead of a positive charge

Answer 1

The most likely reason for the slower migration of the mutant protein Y through the gel-filtration column is that it has a slightly different shape from the wild-type protein, which affects its interaction with the gel matrix.

Step-by-step explanation:

The observation that the mutant version of protein Y runs through the gel-filtration column more slowly than the wild-type protein suggests a change in the hydrodynamic volume of the protein.

The most likely cause for the slower migration is option 4, a change that results in the mutant protein's having a slightly different shape from the wild-type protein.

Shape changes can alter how the protein interacts with the gel matrix, slowing its progress through the column. While a change in charge (options 2 and 5) could potentially affect migration if the column had ion-exchange properties, gel-filtration chromatography primarily separates molecules based on size and shape, not charge.

Options 1 and 3 are less likely because the formation of dimers would usually cause the protein to elute earlier due to increased size, and it is indicated that the substitution is a single amino acid, which should not significantly increase overall size.