Figure 1
The VWA and TSR domains of PfTRAP act together to bind human PDGFRβ. (A) Overlapping constructs containing various PfTRAP domains are represented as a schematic and were similarly used in further experiments. (B) Biotinylated and fluorescently-labeled PfTRAP ectodomain binds preferentially to the HEK293F cells transfected with hPDGFRβ (red) over untransfected cells (blue) within the same culture. Titration experiments (C–H) using increasing dilution of fluorescently labeled fragments of PfTRAP were quantitated as a ratio of binding to transfected versus untransfected cells (gMFI Index) across a 3-log concentration range. Fragments of PfTRAP containing the VWA and TSR domains together bound PDGFRβ strongly across a 3-log range (C, D). While the VWA domain alone showed significant binding to hPDGFRβ at concentrations of 100 nM and above (E), the TSR fragment, the repeat region, or the TSR fragment plus the repeat region did not bind significantly (F–H). Data are the mean ± SD from at least five independent experiments. Analysis by one sample t-test compared to the dashed line (gMFI index expected if no specific binding occurs); *p < 0.05, **p < 0.01, ***p < 0.001. ECD, ectodomain; VWA, von Willebrand factor A domain; TSR, thrombospondin repeat domain.
