Design, synthesis and properties of peptide inhibitors based on BRCA1856-871

Spectroscopic studies on noncovalent binding of nicotinamide-modified BRCA1 (856-871) analogs to calf thymus DNA

Various peptide drugs have entered the market with the development of molecular biology. Peptide drugs are used for treat diseases such as diabetes, breast cancer, and HIV infection. In this study, three nicotinamide-modified peptides were synthesized by modifying the N-terminus of BRCA1 (856-871, Y856R, K862Y, R866W) peptide with three nicotinic acid derivatives using solid-phase peptide synthesis. The results of calf thymus DNA (ctDNA) binding activity indicated that binding constants of BRCA1 (856-871, Y856R, K862Y, R866W) (P0) and three nicotinamide-modified peptides (P1, P2, and P3) to ctDNA were 1.89 × 10³, 2.97 × 10⁴, 7.61 × 10⁴, and 8.09 × 10⁴ L·mol^-1, respectively. The binding affinity of the modified peptides was superior to that of BRCA1 (856-871, Y856R, K862Y, R866W). ΔH^θ < 0 and ΔS^θ < 0 indicated that van der Waals force and hydrogen bond contributed most to peptide-ctDNA binding. Results obtained by Circular dichroism (CD) indicated that peptide binding interaction led to conformational changes in ctDNA. Ultraviolet-visible (UV) spectroscopy, ethidium bromide (EB) competition experiments, DNA melting experiments, and viscosity measurements verified that peptides interacted with ctDNA via groove binding. Ionic strength experiments manifested that electrostatic binding was also involved in peptide-ctDNA binding.

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.