Interaction of bifunctional peptide-carbazole complexes with DNA and antimicrobial activity

Two peptide-carbazole conjugates, CTAT and CNLS, were designed and synthesized using carbazole Schiff base to modify the cell membrane penetrating peptide TAT (47–57) and the nuclear localization peptide NLS at the N terminus. The interaction with ctDNA was investigated by multispectral and agarose gel electrophoresis. And the effects of CNLS and CTAT on the G-quadruplex structure were explored by circular dichroism titration experiments. The results show that both CTAT and CNLS interact with ctDNA in a minor groove binding manner. Both conjugates bind more tightly to DNA than the individual substances CIBA, TAT and NLS. In addition, CTAT and CNLS are capable of unfolding parallel G-quadruplex structures and are potential G-quadruplex unfolding agents. Finally, broth microdilution was performed to test the antimicrobial activity of the peptides. The results showed that CTAT and CNLS had a 4-fold increase in antimicrobial activity compared with the parent peptides TAT and NLS. They could exert antimicrobial activity by disrupting the integrity of cell membrane bilayer and binding to DNA, and could be used as novel antimicrobial peptides for the development of novel antimicrobial antibiotics.