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.
References:
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.
Examples:
TC#	Name	Organismal Type	Example
2.A.70.1.1	*The malonate:Na⁺ symporter, MadLM (MadL, 129aas, 3TMSs; MadM, 255aas, 6TMSs) (Schaffitzel et al.* 1998).**	Bacteria	MadLM of Malonomonas rubra

2.A.70.1.2	*The malonate uptake porter, MdcLM (Chohnan et al., 1999)*	Bacteria	MdcLM of Pseudomonas putida: MdcL (163aas; 4TMSs; Q9Z446) MdcM (254aas; 8TMSs; Q9Z445)