Cellular retinoic acid-binding protein 2 (CRABP2) is a cytosolic, lipid-binding protein thought to bind its natural ligand, all-trans-retinoic acid (atRA) and mediate its delivery to retinoic acid receptors (RARs) within the nucleus (Kleywegt et al. 1994). CRABP2 forms a beta-barrel structure within which a hydrophobic ligand can be accommodated. Once atRA binds to CRABP2, the resulting complex translocates to the nucleus (Budhu & Noy 2002). A ligand activated nuclear-localisation signal appears to be critical for nuclear localisation (Sessler & Noy 2005). Sumoylation of CRABPs is also essential for atRA-induced dissociation of CRABPs from the ER membrane. For CRABP2, the site K102 is sumoylated (Majumdar et al. 2011).