A mutation causes Asp-47 in a protein’s sequence to be replaced by Leu-47. This

Question

A mutation causes Asp-47 in a protein’s sequence to be replaced by Leu-47. This makes the protein inactive and results in a disease. A similar disease is observed if Lys-132 is changed to Val-132. However, a double mutant occurs in some healthy people which still has Leu-47 but also contains the second mutation changing Lys-132 to Val-132 which allows the protein to regain its activity. Give a convincing explanation for why the double mutant regains activity. Use your knowledge of protein folding, NCI’s and protein secondary and tertiary structures in your answer. Explain whether you think it is an effect on secondary OR tertiary structure and why you favor one idea and the other is ruled out!! You may use a picture if it helps your explanation.

Explanation / Answer

Based on the given data,

In single mutant 1:

In single mutant 2:

Here, in both single mutant 1 and 2 conditions, the change in hydrophilic amino acid to hydrophobic amino acid results change in protein structure and function, which results the occurrence of disease. Thus, the Thus, change in the amino acids results change in the hydro properties in the protein.

In double mutant:

In double mutant condition, even though the amino acids are changed, but the 47 position has the hydrophilic amino acid (Lue) and 132 position has hydrophobic amino acid (Val), which regains the properties of protein to normal, and hence it functions in a normal way.

It is an effect on tertiary structure of protein, because most of the proteins show catalytic activity in the tertiary state.   

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