Intracellular carrier for long-chain fatty acids and related active lipids, such as endocannabinoids, that regulate the metabolism and actions of the ligands they bind (PubMed:8608126, PubMed:12540600). In addition to the cytosolic transport, selectively delivers specific fatty acids from the cytosol to the nucleus, wherein they activate nuclear receptors (By similarity). Delivers retinoic acid to the nuclear receptor peroxisome proliferator-activated receptor delta; which promotes proliferation and survival (PubMed:17512406). May also serve as a synaptic carrier of endocannabinoid at central synapses and thus controls retrograde endocannabinoid signaling (PubMed:29531087). Modulates inflammation by regulating PTGES induction via NF-kappa-B activation, and prostaglandin E2 (PGE2) biosynthesis during inflammation (PubMed:29440395). May be involved in keratinocyte differentiation (By similarity). hexadecanoate(out) = hexadecanoate(in) (9Z,12Z)-octadecadienoate(out) = (9Z,12Z)-octadecadienoate(in) (9Z)-octadecenoate(out) = (9Z)-octadecenoate(in) Monomer. Localizes primarily to the cytoplasm. Upon certain ligand binding, a conformation change exposes a nuclear localization motif and the protein is transported into nucleus (By similarity). Secreted by astrocytes, but not by neurons (PubMed:29531087). Widely expressed. Forms a beta-barrel structure that accommodates hydrophobic ligands in its interior. Deficient mice display resistance to diet-induced obesity, decreased adipose tissue and imporved glucose tolerance and insulin sensitivity. Belongs to the calycin superfamily. Fatty-acid binding protein (FABP) family. While human FABP5 can exist as a monomer as well as a domain-swapped dimer, mouse is found only in the monomeric form.