The neuropeptide vasoactive intestinal peptide (VIP) strongly impacts on human pathophysiology and does so through interaction with class II G protein-coupled receptors. We characterized the C-terminus binding site of VIP in the N-terminal ectodomain (N-ted) of the human VPAC1 receptor: (i) The probe ¹²⁵I-[Bpa²⁸]-VIP in which the C-terminal residue (Asn²⁸) is substituted by a photoreactive para-benzoyl-L-Phe (Bpa) was used to photolabel the receptor. After receptor cleavage and Edman sequencing, it was shown that Asn²⁸ of VIP is in contact with Lys¹²⁷ in the receptor N-ted. Taking into account previous data, it follows that the C-terminal and central parts of VIP from Asn²⁸ to Phe⁶ lie in the N-ted. (ii) A 3D model of the N-ted was constructed, the fold being identified as a Sushi domain with two antiparallel sheets and three disulfide bonds. The NMR structure of VIP was then docked into this model by taking into account the constraint provided by photoaffinity experiments with ¹²⁵I-[Bpa²⁸]-VIP. It appeared that VIP runs parallel to the 3-4 antiparallel sheets. (iii) We performed molecular dynamic simulations over 14 ns of the complex between VIP and receptor N-ted and the free N-ted. The structural model of the free N-ted is stable and VIP tends to further stabilize the N-ted structure more especially in the loops connecting the sheets. These structural studies provide a detailed molecular understanding of the VIP-receptor interaction.