Using replica exchange umbrella sampling we calculated free energy profiles for uptake of cholesterol 
and one of its oxysterols (7-ketocholesterol) from an aqueous solution into a high density lipoprotein 
particle. These atomistic molecular dynamics simulations show that both sterols are readily taken up 
from the aqueous solution with comparable free energy minima at the surface of the particle of -17 kcal/mol 
for cholesterol and -14 kcal/mol for 7-ketocholesterol. Moreover, given its preferred position at the 
particle surface, 7-ketocholesterol is expected to be able to participate directly in biological signaling 
processes.