2.A.26 The Branched Chain Amino Acid:Cation Symporter (LIVCS) Family

Characterized members of this family transport all three of the branched chain aliphatic amino acids (leucine (L), isoleucine (I) and valine (V)). They are found in Gram-negative and Gram-positive bacteria and function by a Na+ or H+ symport mechanism. They possess about 440 amino acyl residues and display 12 putative transmembrane helical spanners. Some of these transporters can also take up threonine (Khozov et al. 2023).  BrnQ of E. coli has been reported to be able to take up threonine but not serine.

The generalized transport reaction is:

[L, I, V or T] (out) + [Na+ or H+] (out)  [L, I, V or T] (in) + [Na+ or H+] (in)

This family belongs to the APC Superfamily.



Braun, P.R., H. Al-Younes, J. Gussmann, J. Klein, E. Schneider, and T.F. Meyer. (2008). Competitive inhibition of amino acid uptake suppresses chlamydial growth: involvement of the chlamydial amino acid transporter BrnQ. J. Bacteriol. 190: 1822-1830.

Guardiola, J., M. De Felice, T. Klopotowski, and M. Iaccarino. (1974). Mutations affecting the different transport systems for isoleucine, leucine, and valine in Escherichia coli K-12. J. Bacteriol. 117: 393-405.

Khozov, A.A., D.M. Bubnov, E.D. Plisov, T.V. Vybornaya, T.V. Yuzbashev, G. Agrimi, E. Messina, A.A. Stepanova, M.D. Kudina, N.V. Alekseeva, A.I. Netrusov, and S.P. Sineoky. (2023). A study on L-threonine and L-serine uptake in K-12. Front Microbiol 14: 1151716.

Radi, M.S., J.E. SalcedoSora, S.H. Kim, S. Sudarsan, A.V. Sastry, D.B. Kell, M.J. HerrgÄrd, and A.M. Feist. (2022). Membrane transporter identification and modulation via adaptive laboratory evolution. Metab Eng 72: 376-390.

Reizer, J., A. Reizer and M.H. Saier, Jr. (1994). A functional superfamily of sodium/solute symporters. Biochim. Biophys. Acta 1197: 133-166.

Stucky, K., A. Hagting, J.R. Klein, H. Matern, B. Henrich, W.N. Konings and R. Plapp (1995). Cloning and characterization of brnQ, a gene encoding a low-affinity, branched-chain amino acid carrier in Lactobacillus delbruckii subsp. lactis DSM7290. Mol. Gen. Genet. 249: 682-690.

Tauch, A., T. Hermann, A. Burkovski, R. Krämer, A. Pühler and J. Kalinowski (1998). Isoleucine uptake in Corynebacterium glutamicum ATCC 13032 is directed by the brnQ gene product. Arch. Microbiol. 169: 303-312.

Trip, H., N.L. Mulder, and J.S. Lolkema. (2013). Cloning, expression, and functional characterization of secondary amino acid transporters of Lactococcus lactis. J. Bacteriol. 195: 340-350.


TC#NameOrganismal TypeExample
2.A.26.1.1Branched chain amino acid: Na+ symporter Gram-negative bacteria BraB of Pseudomonas aeruginosa

Branched chain amino acid transporter 2 of 439 aas and 12 TMSs, BrnQ (Guardiola et al. 1974). The brnQ gene can be mutated to give rise to threonine tolerance (Radi et al. 2022). However the wild type protein takes up threonine (in addition to leucine, isoleucine and valine) but with low affinity and high flux (Khozov et al. 2023). 

BrnQ of E. coli

2.A.26.1.2Ile/Val:H+ symporter Gram-negative bacteria BraZ of Pseudomonas aeruginosa
2.A.26.1.3Branched chain amino acid:H+ symporter Gram-positive bacteria BrnQ of Lactobacillus delbrueckii

The branched chain amino acid transporter BrnQ (transports Leu, Ile, Val, Phe, and Met) (Braun et al., 2008).


BrnQ of Chlamydia trachomatis (O84558)


LIVCS family member of 429 aas and 12 TMSs.


LIV transporter of Blautia hydrogenotrophica


Uncharacterized protein of 430 aas and 12 TMSs.


UP of Arcobacter butzleri


LIV transporter of 411 aas and 12 TMSs


LIV transporter of Mycoplasma sp.


LIV transporter of 445 aas and 12 TMSs.


lIV transporter of Desulfovibrio desulfuricans


Branched chain amino acid (Leucine, Isoleucine, Valine) transporter of 456 aas and 12 TMSs, BrnQ (Trip et al. 2013).


BrnQ of Lactococcus lactis