Question

H1 receptor protein in humans is made up of:

• A. 487 Aminoacids
• B. 390 Aminoacids
• C. 445 Aminoacids
• D. 359 Aminoacids

Hint:

- The H1 receptor is a G-protein coupled receptor (GPCR) composed of 487 amino acids. - Understanding the structure of receptors like H1 is crucial in pharmacology, particularly in the design of antihistamines.

Answer 1

The Correct Option is A

Receptor size is usually reported from the cloned gene sequence, since counting the codons in the open reading frame gives an exact residue count rather than an estimate.

1. 487 Aminoacids: Cloning of the human histamine H1 receptor gene shows an open reading frame encoding a 487 residue protein, which includes the seven transmembrane helices along with an unusually long third intracellular loop that adds extra length compared to smaller GPCRs.
2. 390 Aminoacids: A chain this short would be unusually compact for a class A GPCR carrying H1's long intracellular loop region, making this figure too small to fit the known receptor.
3. 445 Aminoacids: This number sits close to the true value but still falls short of the confirmed 487 residue count reported from the cloned H1 receptor sequence.
4. 359 Aminoacids: This is close to the length of some smaller aminergic GPCRs without extended loop regions, but it is too short to match H1's actual sequence.

Based on the confirmed sequence length from the cloned H1 receptor gene, the correct answer is 487 Aminoacids.