Required for assembly of smooth septate junctions (sSJs), together with mesh and Tsp2A (PubMed:22854041, PubMed:26848177). May be important for barrier function of the midgut epithelium. Forms a complex with Tsp2A and mesh (PubMed:26848177). Interacts with mesh; the interaction may be necessary for the localization of both proteins to the cell apicolateral region (PubMed:22854041). Specific to smooth septate junctions. Detected from embryonic stage 12 onwards in midgut and Malpighian tubules (at protein level) (PubMed:22328496, PubMed:22854041, PubMed:26848177). Also detected in the outer epithelial layer of the proventriculus in first instar larvae (at protein level) (PubMed:22854041). Unlikely isoform.