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. In addition to the cytosolic transport, selectively delivers specific fatty acids from the cytosol to the nucleus, wherein they activate nuclear receptors (PubMed:22170058, PubMed:21395585). Delivers retinoic acid to the nuclear receptor peroxisome proliferator-activated receptor delta; which promotes proliferation and survival. May also serve as a synaptic carrier of endocannabinoid at central synapses and thus controls retrograde endocannabinoid signaling. Modulates inflammation by regulating PTGES induction via NF-kappa-B activation, and prostaglandin E2 (PGE2) biosynthesis during inflammation (By similarity). May be involved in keratinocyte differentiation (PubMed:8092987). hexadecanoate(out) = hexadecanoate(in) (9Z,12Z)-octadecadienoate(out) = (9Z,12Z)-octadecadienoate(in) (9Z)-octadecenoate(out) = (9Z)-octadecenoate(in) Monomer. Homodimer. Localizes primarily to the cytoplasm. Upon certain ligand binding, a conformation change exposes a nuclear localization motif and the protein is transported into nucleus (PubMed:24692551). Secreted by astrocytes, but not by neurons (By similarity). Keratinocytes; highly expressed in psoriatic skin (PubMed:8092987). Expressed in brain gray matter (PubMed:21395585). Forms a beta-barrel structure that accommodates the hydrophobic ligand in its interior. Belongs to the calycin superfamily. Fatty-acid binding protein (FABP) family. While mouse FABP5 is found only in the monomeric form, human FABP5 can exist as a monomer as well as a domain-swapped dimer.