Intranuclear delivery of an antiviral peptide mediated by the B subunit of Escherichia coli heat-labile enterotoxin

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Abstract
We report an intracellular peptide delivery system capable of targeting specific cellular compartments. In the model system we constructed a chimeric protein consisting of the nontoxic B subunit of Escherichia coli heat-labile enterotoxin (EtxB) fused to a 27-mer peptide derived from the DNA polymerase of herpes simplex virus 1. Viral DNA synthesis takes places in the nucleus and requires the interaction with an accessory factor, UL42, encoded by the virus. The peptide, designated Pol, is able to dissociate this interaction. The chimeric protein, EtxB-Pol, retained the functional properties of both EtxB and peptide components and was shown to inhibit viral DNA polymerase activity in vitro via disruption of the polymerase-UL42 complex. When added to virally infected cells, EtxB-Pol had no effect on adenovirus replication but specifically interfered with herpes simplex virus 1 replication. Further studies showed that the antiviral peptide localized in the nucleus, whereas the EtxB component remained associated with vesicular compartments. The results indicate that the chimeric protein entered through endosomal acidic compartments and that the Pol peptide was cleaved from the chimeric protein before being translocated into the nucleus. The system we describe is suitable for delivery of peptides that specifically disrupt protein–protein interactions and may be developed to target specific cellular compartments.