63. Which one of the following is not a type of G-protein coupled receptors?
1. 𝐺𝑞
2. 𝐺𝑖
3. 𝐺𝑠
4. 𝐺�

Answer: 4. Gβ

Explanation:

G-protein coupled receptors (GPCRs) are a large family of receptors that mediate various signaling pathways in response to external stimuli. These receptors work by activating G-proteins, which are intracellular proteins that transmit signals from the receptor to various intracellular targets.

• Option 1: Gq – Gq is a type of G-protein coupled receptor that activates phospholipase C (PLC) upon activation. It leads to the production of inositol trisphosphate (IP3) and diacylglycerol (DAG), which are second messengers involved in cellular signaling.

• Option 2: Gi – Gi is another type of GPCR that inhibits adenylyl cyclase, leading to a decrease in cyclic AMP (cAMP) levels. This type of G-protein is involved in various inhibitory signaling pathways.

• Option 3: Gs – Gs is a type of GPCR that activates adenylyl cyclase, leading to an increase in cAMP levels. This type of G-protein is involved in many stimulatory signaling pathways.

• Option 4: Gβ – Gβ is not a type of GPCR. Instead, Gβ is part of the G-protein complex. G-proteins are made up of three subunits: Gα, Gβ, and Gγ. The Gβ subunit is important in signaling, but it is not a receptor itself.

Conclusion:

The correct answer is Option 4: Gβ, as it is a subunit of the G-protein complex and not a type of G-protein coupled receptor. The other options (Gq, Gi, and Gs) are all types of G-protein coupled receptors that play important roles in cellular signaling.