2.A.70 The Malonate:Na+ Symporter (MSS) Family

The monobasic malonate:Na+ symporter of Malonomonas rubra has been functionally and genetically characterized. It consists of two integral membrane proteins, MadL (129 aas) and MadM (255 aas) which exhibit 4 and 7 putative transmembrane spanners, respectively. The transporter is believed to catalyze the electroneutral reversible uptake of H+-malonate with one Na+, and both subunits have been shown to be essential for activity. There is a close two-subunit homologue in Pseudomonas putida (gbAB017138) which is encoded within the malonate decarboxylase gene cluster of this organism (Chohnan et al., 1999). These proteins apparently comprise a new family of secondary carriers as PSI-BLAST searches do not reveal that they are members of other established families. The NapA Na+/H+ antiporter of Enterococcus hirae (spP26235; CPA2 family, TC #2.A.37) appears to be distantly related to MadM.

The transport reaction catalyzed by MadLM is:

H+ malonate (out) + Na+ (out) ⇌ H+ malonate (in) + Na+ (in).

This family belongs to the CPA Superfamily.



Chohnan, S., Y. Kurusu, H. Nishihara, and Y. Takamura. (1999). Cloning and characterization of mdc genes encoding malonate decarboxylase from Pseudomonas putida. FEMS Microbiol. Lett. 174: 311-319.

Schaffitzel, C., M. Berg, P. Dimroth, and K.M. Pos. (1998). Identification of an Na+-dependent malonate transporter of Malonomonas rubra and its dependence on two separate genes. J. Bacteriol. 180: 2689-2693.


TC#NameOrganismal TypeExample
2.A.70.1.1The malonate:Na+ symporter, MadLM (MadL, 129aas, 3TMSs; MadM, 255aas, 6TMSs) Bacteria MadLM of Malonomonas rubra
2.A.70.1.2The malonate uptake porter, MdcLM (Chohnan et al., 1999)BacteriaMdcLM of Pseudomonas putida:
MdcL (163aas; 4TMSs; Q9Z446)
MdcM (254aas; 8TMSs; Q9Z445)