Bracher, SusanneHilger, DanielGuerin, KamilaPolyhach, YevhenJeschke, GunnarKrafczyk, RalphGiacomelli, GiacomoJung, Heinrich2019-06-182019-06-182019-06-182019-03-0710.1038/s41598-019-40516-7https://infoscience.epfl.ch/handle/20.500.14299/157681WOS:000460508600017Secondary transporters exist as monomers, dimers or higher state oligomers. The significance of the oligomeric state is only partially understood. Here, the significance of the trimeric state of the L-carnitine/gamma-butyrobetaine antiporter CaiT of Escherichia coli was investigated. Amino acids important for trimer stability were identified and experimentally verified. Among others, CaiT-D288A and -D288R proved to be mostly monomeric in detergent solution and after reconstitution into proteoliposomes, as shown by blue native gel electrophoresis, gel filtration, and determination of intermolecular distances. CaiT-D288A was fully functional with kinetic parameters similar to the trimeric wild-type. Significant differences in amount and stability in the cell membrane between monomeric and trimeric CaiT were not observed. Contrary to trimeric CaiT, addition of substrate had no or only a minor effect on the tryptophan fluorescence of monomeric CaiT. The results suggest that physical contacts between protomers are important for the substrate-induced changes in protein fluorescence and the underlying conformational alterations.Multidisciplinary SciencesScience & Technology - Other Topicsosmoregulated betaine transportercarnitine metabolismcorynebacterium-glutamicumna+/proline transportercrystal-structurebetpsystemidentificationexpressionstabilitytext::journal::journal article::research article