Betaine / Carnitine / Choline Transporters (BCCT) are a family of prokaryotic transport proteins that are specific for compounds containing a quaternary nitrogen

Quaternary ammonium cation

Quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure NR4+, R being an alkyl group or an aryl group. Unlike the ammonium ion and the primary, secondary, or tertiary ammonium cations, the quaternary ammonium cations are permanently charged,...

 atom. The BCCT proteins contain 12 transmembrane regions and are energized by proton

Proton

The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

 symport. They contain a conserved region with four tryptophans in their central region.

The mammalian betaine transporter (SLC6A12) is regulated by NFAT5 during response to osmotic stress.