Question

Peptide-binding cleft in MHC-I is formed by

• A. \( \alpha_1 \) and \( \alpha_2 \) domains.
• B. \( \alpha_1 \) and \( \alpha_3 \) domains.
• C. \( \alpha_1 \) domain and \( \beta_2 \)-microglobulin.
• D. \( \alpha_2 \) domain and \( \beta_2 \)-microglobulin.

Hint:

In MHC-I molecules, the peptide-binding cleft is formed by the \( \alpha_1 \) and \( \alpha_2 \) domains. \( \beta_2 \)-microglobulin supports the structure but does not contribute to the binding cleft.

Answer 1

The Correct Option is A

In MHC-I molecules, the peptide-binding cleft is formed by the \( \alpha_1 \) and \( \alpha_2 \) domains of the \( \alpha \)-chain. These domains work together to form a groove in which peptides bind. The \( \beta_2 \)-microglobulin supports the structure but does not directly contribute to the peptide-binding cleft. Therefore, statement (A) is correct.
- (B): The \( \alpha_1 \) and \( \alpha_3 \) domains are not involved in forming the peptide-binding cleft. The \( \alpha_3 \) domain contributes to the overall structural stability but not to the peptide binding site. Hence, statement (B) is incorrect.
- (C): The \( \alpha_1 \) domain and \( \beta_2 \)-microglobulin are not responsible for the peptide-binding cleft. While \( \beta_2 \)-microglobulin is essential for the stability of MHC-I, it does not form the cleft. Hence, statement (C) is incorrect.
- (D): The \( \alpha_2 \) domain and \( \beta_2 \)-microglobulin do not form the peptide-binding cleft. The \( \alpha_2 \) domain is involved in interaction with T-cell receptors but not in the peptide binding itself. Hence, statement (D) is incorrect.
Thus, the correct answer is (A).