Question

You are working in a biotech company that has discovered a small molecule drug called H5434. H5434 binds to LDL receptors when they are bound to cholesterol. H5434 binding does not alter the conformation of the LDL receptor's intracellular domain. Interestingly, in vitro experiments demonstrate that addition of H5434 increases the affinity of LDL for cholesterol and prevents cholesterol from dissociating from the LDL receptor even in acidic conditions. Which of the following is a reasonable prediction of what may happen when you add H5434 to cells?

(a) Cytosolic cholesterol levels will remain unchanged relative to normal cells.
(b) Cytosolic cholesterol levels will decrease relative to normal cells.
(c) The LDL receptor will remain on the plasma membrane.
(d) The uncoating of vesicles will not occur.

Answer 1

The correct answer is option (b) "Cytosolic cholesterol levels will decrease relative to normal cells".

Step-by-step explanation:

The main function of LDL receptor's is to mediate the level of low density lipoproteins (LDL, often referred as bad cholesterol) endocytosis to the cells. LDL receptor's recognize when LDL levels are high and pick them into the inside of the cells by picking one molecule at the time. If the drug H5434 prevents cholesterol from dissociating to LDL receptor, the result will be that cytosolic cholesterol levels will decrease relative to normal cells. By preventing the dissociation of LDL with its receptor, the receptors will not be available to take cholesterol into the inside of the cells one at the time, which will result in a decrease of the cytosolic cholesterol levels.