The transferrin receptor of Trypanosoma brucei (TbTfR) is a heterodimer of a glycosylphosphatidylinositol (GPI)-anchored ESAG6 subunit and an ESAG7 subunit. To investigate whether the GPI-anchor is essential for the function of the TbTfR, an ESAG6 with a transmembrane domain instead of a GPI-anchor (ESAG6tmd) was inducibly expressed in bloodstream form trypanosomes. It is shown that the ESAG6tmd is able to dimerise with ESAG7 to form a TbTfR that can bind transferrin. Fractionation experiments clearly demonstrated that the transmembrane-anchored TbTfR is exclusively associated with the membrane fraction. No difference in the uptake of transferrin was observed between trypanosomes inducibly expressing a transmembrane-anchored TbTfR and trypanosomes inducibly expressing a GPI-anchored TbTfR. Differences in glycosylation pattern of ESAG6tmd and native ESAG6 may indicate different intracellular trafficking of transmembrane- and GPI-anchored TbTfRs. The findings suggest that the GPI-anchor is not essential for the function of the TbTfR in bloodstream forms of T. brucei.

布氏锥虫的转铁蛋白受体( Tb TfR) 是由糖基磷脂酰肌醇 (GPI) 锚定的 ESAG6 亚基和 ESAG7 亚基组成的异源二聚体。为了研究 GPI 锚是否对Tb TfR的功能至关重要，在血流形式的锥虫中诱导表达了具有跨膜结构域而不是 GPI 锚（ESAG6tmd）的 ESAG6。结果表明，ESAG6tmd 能够与 ESAG7 形成二聚体，形成可以结合转铁蛋白的Tb TfR。分馏实验清楚地表明，跨膜锚定的TbTfR 仅与膜分数相关。在诱导表达跨膜锚定Tb TfR 的锥虫和诱导表达 GPI 锚定Tb TfR 的锥虫之间没有观察到转铁蛋白的摄取存在差异。ESAG6tmd 和天然 ESAG6 糖基化模式的差异可能表明跨膜和 GPI 锚定的Tb TfR 的细胞内运输不同。研究结果表明，GPI 锚对于T. brucei血流形式中Tb TfR的功能不是必需的。