FIG 4 .

A GPI anchor is sufficient to confer TbERP-dependent trafficking to BiPN. The matched soluble BiPN (A) and BiPN:GPI (B) secretory reporters were each constitutively expressed in each BSF TbERP RNAi cell line as indicated. Specific dsRNA was induced for 72 h (Tet-, open symbols; Tet+, closed symbols). Cells were pulse (10-min)-chase (3 or 4 h) radiolabeled, and reporter trafficking was analyzed by specific immunoprecipitation (anti-BiP) and SDS-PAGE at the indicated chase times. BiPN was immunoprecipitated from both whole-cell lysates (circles) and medium fractions (squares); BiPN:GPI was immunoprecipitated from whole-cell lysates only (circles). BiPN trafficking was assessed by loss of cell-associated reporter and appearance in the medium; BiPN:GPI trafficking was assessed by conversion to the larger Golgi compartment-processed glycoform. (Top) Quantification of cell-associated (circles) and secreted (squares) reporters normalized to total initial signal at T0 (mean ± SEM, n = 3). (Bottom) Representative phosphorimages (1 × 10⁷ cell equivalents per lane). B, native BiP; V, VSG; N, BiPN; I, immature precursor BiPN:GPI; M, mature BiPN:GPI. Note that newly synthesized VSG coprecipitates with native BiP at T0 due to transient physical association during folding/assembly into homodimers (37).