The HTLV-1 SU contains a KPxR motif homologous to the VEGF₁₆₅ exon 8 domain. (A) Sequence alignment between the VEGF₁₆₅ exon 8 domain, the exon 8–like peptides Tuftsin and Tuftsin analog, and the aa 90-94 region of the HTLV-1 SU. The conserved consensus KPxR motif deduced from the alignment is also shown. (B) Local sequence alignment of VEGF₁₆₅ exon 8 sequence with the region of the HTLV/STLV SUs encompassing the KPxR motif. Sequence positions corresponding to conserved and chemically homologous residues between viral sequences are highlighted in dark and light gray, respectively, and the KPxR motif is highlighted in black. The UniProt sequences used for the alignment are, respectively, VEGFA_HUMAN, ENV_HTL1A, ENV_HTLV2, ENV_HTL3P, O41897_9STL1, O09243_9DELA, and Q6XQ01_9DELA. The numbering refers to the complete unprocessed sequences. (C) In vitro binding of exon 8–like peptides to NRP-1 in the BIAcore system. The SU 90-94 peptide, Tuftsin analog (TU-A), or the control peptide (Cont.) was injected (15 μM each) on either recombinant NRP-1 (left panel) or recombinant VEGF-R2 (right panel) previously immobilized on the sensor chip. The sensorgram displays the kinetics of peptide binding after injection (time 0) and is 1 representative experiment of 2 performed. RU indicates resonance unit. (D) In vitro binding of longer SU peptides to NRP-1 in the BIAcore system. Fifteen-mer SU peptides either containing or lacking the KPxR motif (shown in bold) were injected (10 μM each) on recombinant NRP-1 immobilized on the sensor chip. (Left panel) The kinetics of peptide binding to NRP-1 after injection (time 0), which is 1 representative experiment of 2 performed. (Right panel) The binding of the SU 81-95 peptide on NRP-1, corresponding to the maximal RU value of the binding curve, and the absence of binding on BSA or VEGF-R2. (E) The SU 90-94 and exon 8–like peptides compete with VEGF₁₆₅ for NRP-1 binding. (Left panel) Recombinant NRP-1 was injected on immobilized VEGF₁₆₅ in the presence of buffer or of the SU 90-94, Tuftsin, Tuftsin analog (TU-A), or control peptide (100 μM each). The maximal RU value of each curve was used to quantify NRP-1 binding to VEGF₁₆₅, and binding was normalized to condition without peptide (100%). Data are the mean ± SD of 2 independent experiments. (Right panel) Dose-dependent inhibition of the NRP-1/VEGF₁₆₅ interaction by the SU 90-94 and exon 8–like peptides.