Molecular mechanism and cellular function of channel-like SLC26 proteins

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The SLC26 family of multifunctional anion transporters encompasses coupled anion exchanger and anion-dependent motor proteins, but also isoforms that resemble anion channels in macroscopic conduction properties (channel-like SLC26s). Some isoforms are promiscuous in mediating both functions. At present, neither the structural basis nor the physiological role of this functional variability is known. To understand the mechanisms underlying anion channel-like function and to relate it to secondary-active anion exchange we will focus on three isoforms, SLC26A7, SLC26A9 and SLC26A11, that predominantly function in a channel-like mode. We will define all transport modes of SLC26A7, SLC26A9 and SLC26A11 and compare them with an in-depth functional analysis using electrophysiology and fluorescence spectroscopy. Channel-like SLC26s might conduct anions through an anion-selective aqueous permeation pathway or function as uniporter with fast conformational changes. To distinguish between uniporter and channel mechanisms we will employ cysteine accessibility strategies and voltage clamp fluorometry and probe for voltage-dependent displacement ('sensing') currents. To uncover cellular functions of channel-like SLC26 we will study SLC26A11 in heterologous expression systems as well as in renal intercalated cells, one of its native locations. SLC26A11 appears to fulfill its functions in the plasma membrane of native cells, but heterologous expression in cell culture results in predominant lysosomal localization. We will analyze the role of novel accessory subunits and heterodimerization in controlling the SLC26A11 subcellular distribution with a combination of proteomic approaches and light microscopy. We will investigate the role of SLC26A11 in setting cytosolic and intra-organelle [Cl-] and pH in cultured mammalian cells and in intercalated cell lines using fluorescent chloride and pH indicators while manipulating the presence of A11 or identified interactors by overexpression, knock-down, or genome editing.