Neuropilin-1 (NRP1) is a single-pass transmembrane glycoprotein of 923 amino acids, composed of a large extracellular region, a short transmembrane domain and a short cytoplasmic tail (https://www.uniprot.org/uniprot/O14786). Due to alternative splicing or shedding, the extracellular region can be released into circulation as soluble Neuropilin-1.