Recognition and unfolding of human telomeric G-quadruplex by short peptide binding identified from the HRDC domain of BLM helicase

• Published in: RSC advances 2022-08, Vol.12 (34), p.2176-21769
• Main Authors: Sharma, Taniya, Kundu, Nikita, Kaur, Sarvpreet, Chakraborty, Amlan, Mahto, Aman Kumar, Dewangan, Rikeshwer Prasad, Shankaraswamy, Jadala, Saxena, Sarika
• Format: Article
• Language: English
• Subjects: Biological effects; Cellular structure; Chemistry; Crystal structure; Dichroism; Domains; Libraries; Molecular docking; Peptides; Proteins; Recognition
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d2ra03646k

Research in recent decades has revealed that the guanine (G)-quadruplex secondary structure in DNA modulates a variety of cellular events that are mostly related to serious diseases. Systems capable of regulating DNA G-quadruplex structures would therefore be useful for the modulation of various cellular events to produce biological effects. A high specificity for recognition of telomeric G-quadruplex has been observed for BLM helicase. We identified peptides from the HRDC domain of BLM using a molecular docking approach with various available solutions and crystal structures of human telomeres and recently created a peptide library. Herein, we tested one peptide (BLM HRDC peptide) from the library and examined its interaction with human telomeric variant-1 (HTPu-var-1) to understand the basis of G4-protein interactions. Our circular dichroism (CD) data showed that HTPu-var-1 folded into an anti-parallel G-quadruplex, and the CD intensity significantly decreased upon increasing the peptide concentration. There was a significant decrease in hypochromicity due to the formation of G-quadruplex-peptide complex at 295 nm, which indicated the unfolding of structure due to the decrease in stacking interactions. The fluorescence data showed quenching upon titrating the peptide with HTPu-var-1-G4. Electrophoretic mobility shift assay confirmed the unfolding of the G4 structure. Cell viability was significantly reduced in the presence of the BLM peptide, with IC 50 values of 10.71 M and 11.83 M after 72 and 96 hours, respectively. These results confirmed that the selected peptide has the ability to bind to human telomeric G-quadruplex and unfold it. This is the first report in which a peptide was identified from the HRDC domain of the BLM G4-binding protein for the exploration of the G4-binding motif, which suggests a novel strategy to target G4 using natural key peptide segments. Schematic representation of (HTPuvar-1-G4) located at the 3 end, formation of G-quadruplex, model of the G-quadruplex structure, base stacking between G-quadruplex planes, G-quadruplex structure-peptide complex and twisting of G-quadruplex planes upon peptide binding.