Multiple modes for selectivity of transmembrane transport | 10/8/2018 | Staff
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LMU researchers utilized a biophysical approach to understand how bacterial import proteins bind and selectively convey their cargoes across membranes. The results reveal an unexpectedly wide variety of transfer mechanisms.

Many essential cellular functions rely on the selective uptake or export of specific cargoes across membranes. These vital tasks are performed by specialized, membrane-bound, transport proteins. Transporters of this type are required for the import of nutrients from the surrounding medium, the disposal of toxic products or the defense of pathogens. As in any import-export business, the most important aspect of these transport processes is the selection of the appropriate substrates. LMU biophysicist Professor Thorben Cordes and his team have examined how representative members of an important class of transport proteins called bacterial ABC importers select their preferred cargoes. They identified a wide range of binding mechanisms, which are largely dependent on the fact that one domain of the transporters exhibits a surprising degree of structural flexibility. The new findings appear in the online journal eLife.

Transport - ABC - Import - Systems - Recognition

Transport by bacterial ABC import systems begins with the recognition of a potential cargo molecule by a specific substrate binding protein (SBP). Successful binding alters the three-dimensional structure of the binding protein from an open to a closed conformation. It was generally assumed that the conformational change induced by substrate binding dictates the selectivity of substrate transport by enabling the loaded SBP to interact with the transporter subunit, which is responsible for conveying the substrate across the membrane. "However, there were various indications that some molecules bind the SBPs with high affinity but are not subsequently transported across the membrane," says Cordes. "To explore the relationship between binding and transport, we used a spectroscopic method that characterizes both structural changes and dyamics caused by...
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