TABLE 2.

Summary of cholesterol functions in PTCH1 and SMO.

References	Nature of role
Kinnebrew et al. (2021)	PTCH1 moves cholesterol from the outer to the inner leaflet of the membrane in exchange for potassium ion export
Huang et al. (2018)	Cholesterol mediated Smo activation involves the rearrangement of CRD orientation and a cation-lock opening in the TMD.
Byrne et al. (2016)	Cholesterol was proposed as an endogenous SMO ligand capable of regulating Hh signaling engages the CRD groove
Zhang et al. (2018)	PTCH1 restricts the access of cholesterol to SMO by controlling the flipping of cholesterol in plasma membrane lipid bilayers.
Hu and Song, (2019)	PTCH1 control the accessibility or enzymatic activity of unknown protein(s) responsible for cholesterol modification of Smoothened
Kinnebrew et al. (2019)	PTCH1 inhibits SMO by reducing accessible cholesterol from the ciliary membrane
Radhakrishnan et al. (2020)	PTCH1 functions as a membrane remodeling machine to inhibit SMO by changing the cholesterol composition of the ciliary membrane
Myers et al. (2017)	Regulation of SMO by protecting its 7TM domain from cholesterol, or by providing an inhibitor that blocks this cholesterol activation