Heligmosomoides polygyrus, a mouse parasite, modulates host immunity by secreting modular transforming growth factor-β (TGFβ) mimics (TGMs). The agonist TGM1 interacts with TGFBR1, TGFBR2, and the co-receptor CD44 through domains D1/2, D3, and D4/5, respectively. In contrast, the antagonist TGM6, which lacks D1/2, but retains TGFBR2 binding through D3, targets different cells compared to TGM1. The TGM6 co-receptor is unknown. Using X-ray crystallography and binding studies, we show that TGM6 preferentially binds mouse TGFBR2 over human TGFBR2, and that this is essential for its antagonistic function. We identified low-density lipoprotein receptor-related protein 1 (LRP1) and betaglycan (TGFBR3) as co-receptors for TGM6. LRP1 enhances TGM6 efficacy and is required for its antagonistic effect by promoting TGFBR2 lysosomal degradation, whereas betaglycan counteracts TGM6 in a TGFBR2-dependent manner. The modular organization of TGMs enabled us to design TGM1/6 chimeras or TGM-D3 fusion with an affibody that recognizes a specific cell-surface receptor, thereby altering cell-type specificity and functionality. Furthermore, we developed a TGFBR2 nanobody that, on its own, has no inhibitory effect but, when fused to a receptor antibody, antagonizes TGFβ by blocking TGFβ receptor interaction in a cell-selective manner. Thus, we designed programmable agents that modulate TGFβ signaling only in co-receptor-expressing cells.
Dinther et al. (Mon,) studied this question.