If a mutation to a G protein α subunit slows down the rate of GTP hydrolysis, what is the most likely outcome? The α subunit will remain bound to the GPCR for longer, resulting in increased downstream signaling The α subunit will not bind adenylate cyclase, resulting in decreased downstream signaling The α subunit will remain active for longer, resulting in increased downstream signaling The α subunit will not exchange GDP for GTP, resulting in decreased downstream

The most likely outcome if a mutation to a G protein α subunit slows down the rate of GTP hydrolysis is that the α subunit will remain active for longer, resulting in increased downstream signaling.

Here's why:

1. G proteins are involved in signal transduction in cells. They are activated when a G protein-coupled receptor (GPCR) binds to a ligand (a molecule that binds to another, usually larger, molecule).

2. The G protein is made up of three subunits: α, β, and γ. The α subunit is bound to GDP in the inactive state.

3. When the GPCR binds to a ligand, it causes a conformational change in the G protein, causing the α subunit to exchange GDP for GTP, activating the G protein.

4. The activated α subunit then dissociates from the β and γ subunits and can interact with other proteins in the cell to trigger a signaling cascade, leading to a cellular response.

5. The α subunit has an intrinsic GTPase activity, meaning it can hydrolyze the bound GTP back to GDP. This inactivation step is crucial for turning off the signal.

6. If a mutation slows down the rate of GTP hydrolysis, the α subunit will remain in its active, GTP-bound state for longer. This means it can continue to interact with other proteins and trigger downstream signaling for a longer period, leading to increased downstream signaling.