A study on endonuclease BspD6I and its stimulus-responsive switching by modified oligonucleotides.

Nicking endonucleases (NEases) selectively cleave single DNA strands in double-stranded DNAs at a specific site. They are widely used in bioanalytical applications and in genome editing; however, the peculiarities of DNA-protein interactions for most of them are still poorly studied. Previously, it has been shown that the large subunit of heterodimeric restriction endonuclease BspD6I (Nt.BstD6I) acts as a NEase. Here we present a study of interaction of restriction endonuclease BspD6I with modified DNA containing single non-nucleotide insertion with an azobenzene moiety in the enzyme cleavage sites or in positions of sugar-phosphate backbone nearby. According to these data, we designed a number of effective stimulus-responsive oligonucleotide inhibitors bearing azobenzene or triethylene glycol residues. These modified oligonucleotides modulated the functional activity of Nt.BspD6I after cooling or heating. We were able to block the cleavage of T7 phage DNA by this enzyme in the presence of such inhibitors at 20-25°C, whereas the Nt.BspD6I ability to hydrolyze DNA was completely restored after heating to 45°C. The observed effects can serve as a basis for the development of a platform for regulation of NEase activity in vitro or in vivo by external signals.