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Updated: Aug 7, 2025

Characterization of Membrane Transporters by Heterologous Expression in E. coli and Production of Membrane Vesicles
Published on: December 31, 2019
Membrane-anchored substrate binding proteins are deployed in secondary TAXI transporters
Anja Roden1, Melanie K Engelin1, Klaas M Pos1
1Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue-Strasse 9, D-60438 Frankfurt am Main, Germany.
Abstract:
Substrate-binding proteins (SBPs) are part of solute transport systems and serve to increase substrate affinity and uptake rates. In contrast to primary transport systems, the mechanism of SBP-dependent secondary transport is not well understood. Functional studies have thus far focused on Na+-coupled Tripartite ATP-independent periplasmic (TRAP) transporters for sialic acid. Herein, we report the in vitro functional characterization of TAXIPm-PQM from the human pathogen Proteus mirabilis. TAXIPm-PQM belongs to a TRAP-subfamily using a different type of SBP, designated TRAP-associated extracytoplasmic immunogenic (TAXI) protein. TAXIPm-PQM catalyzes proton-dependent α-ketoglutarate symport and its SBP is an essential component of the transport mechanism. Importantly, TAXIPm-PQM represents the first functionally characterized SBP-dependent secondary transporter that does not rely on a soluble SBP, but uses a membrane-anchored SBP instead.
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