FABP are thought to play a role in the intracellular transport of long-chain fatty acids and their acyl-CoA esters. FABPs are important elements related to the hibernating state in mammals. Up-regulated during hibernation in brown adipose tissue and skeletal muscle compared with levels in euthermic bats. Forms a beta-barrel structure that accommodates the hydrophobic ligand in its interior. Belongs to the calycin superfamily. Fatty-acid binding protein (FABP) family.