Sodium-coupled glutamate transporters exhibit an evolutionarily conserved trimeric structure. To understand the functional significance of this architecture, we thought to define residues necessary for oligomerisation with the aim to engineer monomeric transporters or transporters with different oligomerisation states. The recently published high resolution structure of the P. horikoshii glutamate transporter showed the transmembranal helices 2, 4 and 5 in contact with neighboring subunits. Within the contact area, a subset of residues may contribute the majority of binding energy. Working with the E. coli isoform, ecgltP, we identified charged or polar amino acids within these helices that might play a role in intermolecular interactions and mutated them to residues with different charge or polarity. WT and mutant ecgltP were expressed in X. laevis oocytes, [35S]methionine-labeled, and studied with blue native (BN) PAGE. So far, we have found three mutants H50F, H50E, and H181F ecgltP, that showed an increased percentage of monomers and dimers. Additionally, we made a virtual alanine scan predicting residues M56, E130, G138, P184 and E194 as