Guanidinium ion exporter. Couples guanidinium export to the proton motive force, exchanging one guanidinium ion for two protons (PubMed:29507227). Overexpression leads to resistance to a subset of toxic quaternary ammonium compounds such as cetylpyridinium, cetyldimethylethyl ammonium and cetrimide cations (PubMed:11948170). Homodimer. The subunits assemble with antiparallel topology. Transcriptionally regulated by guanidine, via a guanidine-sensing riboswitch. Belongs to the drug/metabolite transporter (DMT) superfamily. Small multidrug resistance (SMR) (TC 2.A.7.1) family. Gdx/SugE subfamily. Was originally (PubMed:8096175) thought to suppress a groEL mutation and mimic the effect of groE overexpression. This was later shown (PubMed:11948170) to be probably due to an artifact. Extended N-terminus. Extended N-terminus.