Malonate:Sodium symporter

The Malonate:Na⁺ Symporter Family is a group of transport proteins belonging to the CPA superfamily. These proteins are composites with constituents ranging in size from 129 to 255 amino acyl residues and exhibiting 4 to 7 transmembrane segments. A representative list of proteins belonging to the MSS family can be found in the .

MadLM

One constituent member of the MSS family, the monobasic malonate:Na⁺ symporter of Malonomonas rubra, has been functionally and genetically characterized. It consists of two integral membrane proteins, MadL and MadM 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, which is encoded within the malonate decarboxylase gene cluster of this organism. The NapA Na⁺/H⁺ antiporter of Enterococcus hirae also appears to be distantly related to MadM.
The transport reaction catalyzed by MadLM is:

H⁺ malonate + Na⁺ ⇌ H⁺ malonate + Na⁺.