Structural Stringency and Optimal Nature of Cholesterol Requirement in the Function of the Serotonin Receptor.

The role of membrane cholesterol in modulating G protein-coupled receptor (GPCR) structure and function has emerged as a powerful theme in contemporary biology. In this paper, we report the subtlety and stringency involved in the interaction of sterols with the serotonin receptor. For this, we utilized two immediate biosynthetic precursors of cholesterol, 7-dehydrocholesterol (7-DHC) and desmosterol, which differ with cholesterol merely in a double bond in their chemical structures in a position-dependent manner. We show that whereas 7-DHC could not support the ligand binding function of the serotonin receptor in live cells, desmosterol could partially support it. Importantly, depletion and enrichment of membrane cholesterol over basal level resulted in an increase and reduction of the basal receptor activity, respectively. These results demonstrate the relevance of optimal membrane cholesterol in maintaining the activity of the serotonin receptor, thereby elucidating the relevance of cellular cholesterol homeostasis.