P1 – Comprehensive structural description of SLC26 membrane transport and its modulation

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Cellular physiology critically depends on the generation and maintenance of chloride and bicarbonate ion gradients across membranes. Solute carriers from the SLC26 family play an important role in this process as illustrated by their causative role in certain pathologies. Recent structures uncovered the overall protein architecture and revealed a unique arrangement of protomers in the dimer including a swapped arrangement of the cytoplasmic STAS domain. Further functional analysis highlighted a role of the STAS domain in accelerating transport, and demonstrated cooperative interactions between the protomers in the dimer. However, as the available structures do not describe a complete translocation cycle, it has remained unclear how transport, its modulation, and the cooperativity between protomers are integrated. We aim to provide an extensive structural and mechanistic framework for addressing these questions. We will first delineate the complete conformation space of mammalian SLC26 transporters in a lipid environment using a unique methodological approach involving: (i) small antibodies, to arrest the proteins in discrete conformations; and (ii) single-particle cryo-EM for structure determination. Subsequent structures of transporters with protomers in opposite conformations will uncover the basis for functional cooperativity in the SLC26 dimer. Finally, structural and functional interrogations of the dimer interfaces involving the STAS domain will result in a mechanistic appreciation of STAS-mediated modulation of transport. Together with complementary collaborations within the Research Unit addressing further functional and dynamic aspects, we expect to provide unprecedented mechanistic insights in SLC26 transport.