| Functional Category | Key Information | Evidence Source |
|---|---|---|
| Primary Function | A0A2R9CAF4 from *Pan paniscus* is best interpreted as the bonobo ortholog of SLC26A11, a sodium-independent sulfate anion transporter in the SLC26/SulP family. Recent mechanistic work identifies SLC26A11 as the lysosomal sulfate exporter and a dual-function protein capable of both coupled sulfate transport and chloride conductance. | (pqac-00000003, pqac-00000008) |
| Substrate Specificity | Direct functional studies show transport or strong competition by sulfate, chloride, oxalate, thiosulfate, selenate, and molybdate; iodide, acetate, and chloride inhibit sulfate uptake to lesser extents, while phosphate and bicarbonate show little to no effect in the reconstituted assay. Earlier family summaries also list Cl−, HCO3−, SO4^2−, and oxalate for SLC26A11/KBAT. | (pqac-00000002, pqac-00000014) |
| Transport Mechanism | SLC26A11 operates primarily as an electroneutral proton:sulfate/chloride exchanger. The most parsimonious model is symport of 1 H+ with 1 SO4^2− coupled to antiport of 1 Cl−. Independent electrophysiology further shows a chloride-selective channel-like conductance gated by proton/sulfate transport, establishing dual transporter-channel behavior. | (pqac-00000002, pqac-00000008) |
| Kinetic Parameters | Apparent sulfate transport KM in proteoliposomes: 39.7 ± 5.5 µM under a strong pH gradient (pHout 5.0; pHin 7.5). Apparent KD values from DSF: chloride 6.0 ± 1.4 mM at pH 5.0 and 5.3 ± 0.7 mM at pH 7.5; sulfate 57 ± 11 µM at pH 5.0 versus 2.9 ± 0.4 mM at pH 7.5, showing strong pH-dependent sulfate selectivity. | (pqac-00000003, pqac-00000007) |
| Subcellular Localization | In mammalian cells, SLC26A11 localizes predominantly to lysosomes, with significant overlap with Lamp1 and minimal overlap with the ER marker calnexin. Co-expression with SLC26A4 or SLC26A7 does not relocalize it, and no evidence for heterodimerization with those paralogs was found. A fraction reaches the plasma membrane in Sf9 insect cells, enabling electrophysiology, but lysosomal localization is the dominant mammalian pattern. | (pqac-00000000, pqac-00000001, pqac-00000010, pqac-00000007) |
| Structural Features | SLC26A11 forms a homodimer. Each protomer contains 14 transmembrane helices organized into transport and scaffold domains plus a cytosolic STAS domain. The STAS domains are domain-swapped between protomers. SLC26A11 has a notably compact STAS domain, an alternative N-glycosylation site at Asn-294 in the TM7-8 loop, and a kinked TM7 that exposes a potential SH3-binding motif. | (pqac-00000002, pqac-00000004) |
| Biological Processes | The transporter participates in lysosomal sulfate homeostasis and catabolite clearance. Sulfate produced by lysosomal degradation and sulfatase reactions must be exported to prevent product accumulation and competitive inhibition of sulfatases; SLC26A11 is proposed to mediate this efflux using the lysosomal proton gradient. It is also discussed as contributing to lysosomal chloride homeostasis and transport-rate optimization. | (pqac-00000003, pqac-00000008, pqac-00000013) |
| Tissue Expression | SLC26A11 is broadly expressed, with highest reported expression in brain and additional expression in kidney/intercalated cells, pancreatic ducts, endothelial cells, and other tissues. Broad distribution is consistent with a housekeeping role in lysosomal function. | (pqac-00000003, pqac-00000014, pqac-00000008) |
| Unique Features | A distinctive Glu-320 residue, unique among mammalian SLC26 family members at the aligned position, acts as a pH-sensitive determinant of substrate preference. Protonation of Glu-320 selectively increases sulfate affinity by nearly two orders of magnitude while leaving chloride affinity largely unchanged, explaining how SLC26A11 favors sulfate export from the acidic lysosomal lumen despite high luminal chloride. | (pqac-00000004, pqac-00000007, pqac-00000008) |
| Clinical Relevance | SLC26A11 chloride currents have been implicated in pathological neuronal swelling and ischemia-associated brain edema under acidic conditions, making SLC26A11 a potential therapeutic target. More broadly, recent sulfate-transporter work in related SLC26 members underscores the physiological importance of sulfate homeostasis in humans, including musculoskeletal and cartilage biology, which strengthens interest in SLC26A11 as a lysosomal sulfate-handling protein. | (pqac-00000013, pqac-00000011) |


*Table: This table summarizes the current functional annotation for bonobo A0A2R9CAF4 as the SLC26A11 ortholog, integrating recent structural, mechanistic, localization, and clinical evidence. It is useful for quickly mapping primary function, substrate handling, localization, and biological significance to specific cited sources.*