The fd phage and a peptide derived from its p8 coat protein interact with the HIV-1 Tat-NLS and inhibit its biological functions

Filamentous fd bacteriophages are used to construct phage-display peptide libraries, which have been instrumental in selecting peptides that interact with specific domains within target molecules. Here we demonstrate that the fd bacteriophage itself, as well as NTP8 - a synthetic peptide derived from it and bearing amino acids 1-20 of the phage p8 protein - interact with the nuclear localization signal (NLS) of the HIV-1 Tat protein. Accordingly, fd bacteriophage and the NTP8 peptide inhibit binding mediated by the Tat-NLS to the nuclear-import receptor importin β and Tat-NLS-mediated translocation into cell nuclei. The NTP8 peptide, at 100 μM concentration, also caused about 50% inhibition of HIV-1 propagation in cultured cells. The fd bacteriophage prevents heparan sulfate proteoglycans-mediated uptake of extracellular Tat by target cells and consequently transactivation of a chloramphenicol acetyltransferase (CAT) reporter gene. A BSA-NTP8 conjugate inhibits Tat-NLS-mediated binding to heparin immobilized on a BIAcore surface. BLAST analysis of the NTP8 amino-acid sequence revealed similarity to sequences in several human proteins, including ADA2 and CD53.