The amino acid substitution of Val for Glu in Hemoglobin S results in aggregation of the Protein because of ……... interaction between molecules .

Options

A. Covalent
B. disulfide
C. hydrogen bonding
D. hydrophobic

Answer

To solve the question regarding the amino acid substitution of Valine (Val) for Glutamic acid (Glu) in Hemoglobin S and its resulting aggregation, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Context**:
- Hemoglobin S is a variant of hemoglobin that is associated with sickle cell disease. The substitution of Valine for Glutamic acid is a key mutation that leads to the disease.

2. **Identify the Amino Acids**:
- Glutamic acid (Glu) is a polar, negatively charged amino acid, while Valine (Val) is a non-polar, hydrophobic amino acid. This change in properties is crucial for understanding the interactions that lead to protein aggregation.

3. **Analyze the Interaction Types**:
- The question asks about the type of interaction that causes the aggregation of the hemoglobin molecules. The options provided are:
- a) Covalent
- b) Disulfide
- c) Hydrogen bonding
- d) Hydrophobic interactions

4. **Evaluate Each Option**:
- **Covalent Interactions**: These involve the sharing of electron pairs between atoms. They are not the primary cause of protein aggregation in this case.
- **Disulfide Bonds**: These are covalent bonds formed between cysteine residues. They are not relevant here since neither Val nor Glu contains cysteine.
- **Hydrogen Bonds**: These are interactions between polar molecules. While they can play a role in protein structure, they do not primarily drive the aggregation in this context.
- **Hydrophobic Interactions**: These occur between non-polar molecules in an aqueous environment. The substitution of Val (hydrophobic) for Glu (polar) leads to a loss of solubility and promotes aggregation due to the tendency of hydrophobic regions to avoid water.

5. **Conclusion**:
- The correct answer is **d) Hydrophobic interactions**. The aggregation of Hemoglobin S occurs because the non-polar Valine residues tend to cluster together, leading to the formation of insoluble aggregates.

### Final Answer:
The amino acid substitution of Val for Glu in Hemoglobin S results in aggregation of the protein because of **hydrophobic interactions** between molecules.