The breast cancer resistance protein (BCRP) belongs to the G-branch of the ABC-transporter family (ABCG2). In contrast to most other ABC-proteins, BCRP consists of only one transmembrane domain (TDM) with one nucleotide binding fold (NBF) at its C-terminus.
Because of this structural characteristic BCRP as well as other ABC-transporters with only one TMD are termed half transporters.
To achieve functional activity these transporters have to form hetero- or homodimers.
BCRP is involved in the multidrug resistance of certain tumors and transports endogenous compounds like cholesterol and steroid hormones.