Membrane-translocating peptides

A method for isolating a membrane-translocating peptide (MTP) from an in vitro peptide library, comprising the steps of:

• a) forming the in vitro peptide library comprising a plurality of nucleic acid-peptide complexes, each peptide of the nucleic acid-peptide complex comprising a candidate membrane translocation peptide by:
• expressing in vitro a plurality of nucleic acid constructs, each nucleic acid construct comprising a nucleic acid target sequence and a promoter sequence operably linked to a nucleic acid coding sequence, said nucleic acid coding sequence encoding a peptide of between 2 and 50 amino acid residues and a nucleic acid binding peptide capable of binding in cis to the nucleic acid target sequence, such that expression of the nucleic acid coding sequences leads to formation of the plurality of nucleic acid-peptide complexes through cis-binding of the nucleic acid binding peptide to the nucleic acid target sequence,
• b) incubating the in vitro peptide library with a population of membrane-encapsulated compartments under conditions designed to allow translocation into the compartment by the nucleic acid-peptide complexes;
• c) removing any nucleic acid-peptide complexes that remain unassociated with the membrane-encapsulated compartments;
• d) removing nucleic acid-peptide complexes that are bound to the surface of the membrane-encapsulated compartments, but which have not been internalized by exposing the membrane-encapsulated compartments to a protease or a nuclease;
• e) recovering any internalized nucleic acid-peptide complexes from within the membrane-encapsulated compartments;
• and
• f) isolating and characterising the peptide encoded by the nucleic acid of the internalized nucleic acid-peptide complex.