The 18 kDa translocator protein (TSPO), originally identified as a peripheral-type benzodiazepine receptor (BZRP), is a drug- and cholesterol-binding protein found at particularly high levels in steroid synthesising cells such as those of the adrenal glands and testes (Lin et al. 1993, De Souza et al. 1985). TSPO is localised to the outer mitochondrial membrane (Anholt et al. 1986) and could facilitate the transport of cholesterol (CHOL) to the inner mitochondrial membrane where the first step of steroidogenesis occurs (review - Papadopoulos et al. 2015). The peripheral-type benzodiazepine receptor-associated protein 1 (TSPOAP1, aka BZRAP1, PRAX1) is a cytosolic protein that specifically interacts with TSPO (Galiegue et al. 1993) but its role is undetermined.