Dimerization in the SLC12 family: Structural and biochemical perspectives

Solute carrier proteins (SLCs) are essential membrane protein transporters of small solutes. Among them, the SLC12 family is known to facilitate transport of ions. Members of the SLC12 family ensure cell homeostasis by co-transporting chloride alongside sodium and/or potassium across the plasma membrane. The majority of SLC12 proteins are well described, and a recent surge in structural studies facilitated by cryo-electron microscopy revealed molecular details of their function. These include multiple conformations of the transporters, covering a range of functional states and providing a window into the ion transport mechanism. Yet, only limited knowledge exists regarding their dimerization or higher order oligomerization and its role in regulation, despite SLC12 proteins consistently operating as dimers. In this review, we highlight the structural knowledgebase established in recent years and summarize the varying dimerization mechanisms. Altogether, it is becoming increasingly clear that large conformational changes in dimeric arrangements deserve attention, alongside other understudied areas like lipid interactions, nucleotide or N-terminal binding to the dimerization domains, and potential roles of the less described member SLC12A9.