Structural basis for functional interactions in dimers of SLC26 transporters

Eva A Jaumann,Yung-Ning Chang,Eric R Geertsma,Julia Hartmann,Gerhard Hummer,Dominik Oliver,Katrin Reichel,Benesh Joseph

doi:10.1038/s41467-019-10001-w

Eva A Jaumann, Yung-Ning Chang + Show 6 more

Open Access

https://doi.org/10.1038/s41467-019-10001-w

Copy DOI

Abstract

The SLC26 family of transporters maintains anion equilibria in all kingdoms of life. The family shares a 7 + 7 transmembrane segments inverted repeat architecture with the SLC4 and SLC23 families, but holds a regulatory STAS domain in addition. While the only experimental SLC26 structure is monomeric, SLC26 proteins form structural and functional dimers in the lipid membrane. Here we resolve the structure of an SLC26 dimer embedded in a lipid membrane and characterize its functional relevance by combining PELDOR/DEER distance measurements and biochemical studies with MD simulations and spin-label ensemble refinement. Our structural model reveals a unique interface different from the SLC4 and SLC23 families. The functionally relevant STAS domain is no prerequisite for dimerization. Characterization of heterodimers indicates that protomers in the dimer functionally interact. The combined structural and functional data define the framework for a mechanistic understanding of functional cooperativity in SLC26 dimers.

Highlights

The solute carrier family 26 (SLC26) family of transporters maintains anion equilibria in all kingdoms of life
We integrated pulsed electron–electron double resonance (PELDOR, known as double electron–electron resonance) distance measurements and in vitro transport studies with structural modeling and refinement using molecular dynamics (MD) simulation to determine the architecture of the membrane-embedded SLC26 dimer and characterize its functional relevance
To define the SLC26Dg dimer interface, we used interspin distance constraints derived from PELDOR experiments

Summary

Introduction

The family shares a 7 + 7 transmembrane segments inverted repeat architecture with the SLC4 and SLC23 families, but holds a regulatory STAS domain in addition. We resolve the structure of an SLC26 dimer embedded in a lipid membrane and characterize its functional relevance by combining PELDOR/DEER distance measurements and biochemical studies with MD simulations and spin-label ensemble refinement. Recent structures subsequently confirmed this oligomeric state for SLC417–19 and SLC2321,22 proteins and indicated that in both families the gate domains form the main interaction surface between protomers, though each family appears to hold a distinct dimer interface. We integrated pulsed electron–electron double resonance (PELDOR, known as double electron–electron resonance) distance measurements and in vitro transport studies with structural modeling and refinement using molecular dynamics (MD) simulation to determine the architecture of the membrane-embedded SLC26 dimer and characterize its functional relevance

Methods

Results

Conclusion