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Feline leukemia virus subgroup C cellular receptor family, member 2 (FLVCR2) is a choline transporter belonging to the major facilitator superfamily (MFS).[5] It is a uniporter transmembrane protein that transports choline across the plasma membrane via a concentration gradient. FLVCR2 is highly enriched in endothelial cells of the blood-brain barrier but is also expressed in peripheral tissues such as the small intestine where it absorbs dietary choline.[6][7][8] At the blood-brain barrier, FLVCR2 is the primary transporter of choline responsible for approximately 60% of the brains supply.[5]
Mutations in FLVCR2 have been associated with proliferative vasculopathy and hydranencephaly-hydrocephaly syndrome (Fowler syndrome).[9]
In 2009, the feline FLVCR2 ortholog was the first identified as a receptor of the Feline leukemia virus (FeLV) in cats.[10] The following year, it was characterised as a heme transporter as it was shown to bind heme, increase heme transport.[11] However, in 2024 it was shown to transport choline both in vivo and in vitro through the use of radiolabel choline transport assays and structural characterisation showing choline bound.[5] FLVCR2's role in disease and interactions with heme remains an ongoing investigation.
FLVCR2 is a 60 kDa protein that adopts the canonical MFS fold consisting of 12 transmembrane alpha-helices with no significant extracellular structures or glycosylation. [5][12] These helices are organized into two distinct pseudo-symmetrical bundles: the N-terminal and C-terminal domains—which are both oriented towards the cytosol. [5] Together, these domains pack against one another to create a central aqueous cavity that serves as the translocation pathway for substrates such as choline. The protein operates through an alternating-access mechanism, often described as a "rocker-switch" motion, where the helices undergo conformational shifts to transition the central pore between outward-facing, occluded, and inward-facing states.
↑Yasujima T, Namba C, Azuma Y, Shinoda Y, Matake I, Yamasaki M, etal. (August 2025). "The role of FLVCR1 and FLVCR2 in choline transport in the Caco-2 intestinal epithelial cell model and rat small intestine". Biochimica et Biophysica Acta. Molecular Basis of Disease. 1871 (6) 167883. doi:10.1016/j.bbadis.2025.167883. PMID40320184.
