*3.1. Characterization of Heparin-Cy5 Binding to Ookinetes*

Flow cytometry analysis showed binding of heparin-Cy5 to ookinetes obtained ex vivo from mouse blood infected with the *P. berghei* CTRP-GFP transgenic line (Figure 1a,b), which expresses GFP when reaching ookinete stage. Fluorescence images indicated the binding of heparin-Cy5 to discrete areas on the ookinete (Figure 1c), which suggests clustering of heparin receptors. *‐* ‐ ‐ 

‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ μ **Figure 1.** Heparin-Cy5 binding to ookinetes. (**a**) Flow cytometry plot showing heparin-Cy5 signal in green fluorescent protein (GFP)-expressing *P. berghei* ookinetes. GFP-negative events correspond mostly to red blood cells (see Figure S1 for gating strategy). c1 to c4 refer to the individual events reported in panel **c**. (**b**) Difference in Cy5 median intensity between GFP-expressing ookinetes and GFP-negative cells. (**c**) Fluorescence images of the flow cytometry events indicated in panel **a**. The merges of the bright field (BF) image with the fluorescence of heparin, nuclei, GFP, and all three of them, are indicated as merge-1 to merge-4, respectively. Size bars represent 7 µm.

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