Question

Endoplasmic targeting signal is

• A. Lys-Asp-Glu-Leu
• B. Pro-Lys-Ala-Lys-Val
• C. Ser-Lys-Leu
• D. Asp-Glu-Leu-Lys

Hint:

The single-letter code for Lys-Asp-Glu-Leu is KDEL.
This is a standard retention signal for soluble endoplasmic reticulum proteins.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Proteins synthesized in the cytosol are targeted to specific organelles by short amino acid sequences called signal peptides or targeting signals.

Step 2: Detailed Explanation:
Soluble proteins resident to the lumen of the endoplasmic reticulum (ER) contain a specific C-terminal retention/retrieval signal sequence.
This tetrapeptide sequence is Lys-Asp-Glu-Leu (commonly abbreviated in single-letter code as KDEL).
If an ER-resident protein escapes to the cis-Golgi network, it binds to KDEL receptors, which package the protein into COPI-coated vesicles for retrograde transport back to the ER.

Step 3: Final Answer:
The correct option is 1, which corresponds to Lys-Asp-Glu-Leu.