A combined experimental and computational study additionally took into account the quaternary structure of LL-37 to investigate LL-37's channel-forming properties . Using X-ray crystallography, a tetrameric conformation of LL-37 was observed (PDB ID 7pdc) , which was consistent with circular dichroism experiments indicating oligomerization and toroidal pore formation . The experimentally determined tetramer structure was used in molecular dynamics (MD) simulations embedded within a model of the Gram-negative inner membrane (POPE:POPG at a ration of 3:1) and homogeneous bilayers of POPE, POPG, and POPC. The tetramer was more stable in the Gram-negative inner membrane than in POPC, which explains LL-37's selectivity for bacterial membranes over mammalian ones .