XL-protein develops and commercializes its proprietary PASylation® technology to extend the plasma half-life of biopharmaceuticals. The genetic fusion (or chemical conjugation) with conformationally disordered amino acid sequences composed of the three small residues Pro, Ala, and/or Ser ('PASylation') provides a simple way to attach a solvated biopolymer with large hydrodynamic volume to a therapeutic protein or peptide. This polypeptide adopts a bulky random coil structure, which significantly increases the size of the biopharmaceutical. By this means the typically rapid clearance of the biologically active component via kidney filtration is retarded by 1-2 orders of magnitude, depending on the length of the PAS tag. Compared with other strategies to prolong the plasma half-life of biologics the PASylation technology provides numerous advantages.