title: Differential inhibitory activities and stabilisation of DNA aptamers against the SARS coronavirus helicase.
abstract: The helicase from severe acute respiratory syndrome coronavirus (SARS-CoV) possesses NTPase, duplex RNA/DNA-unwinding and RNA-capping activities that are essential for viral replication and proliferation. Here, we have isolated DNA aptamers against the SARS-CoV helicase from a combinatorial DNA library. These aptamers show two distinct classes of secondary structure, G-quadruplex and non-G-quadruplex, as shown by circular dichroism and gel electrophoresis. All of the aptamers that were selected stimulated ATPase activity of the SARS-CoV helicase with low-nanomolar apparent K(m) values. Intriguingly, only the non-G-quadruplex aptamers showed specific inhibition of helicase activities, whereas the G-quadruplex aptamers did not inhibit helicase activities. The non-G-quadruplex aptamer with the strongest inhibitory potency was modified at the 3'-end with biotin or inverted thymidine, and the modification increased its stability in serum, particularly for the inverted thymidine modification. Structural diversity in selection coupled to post-selection stabilisation has provided new insights into the aptamers that were selected for a helicase target. These aptamers are being further developed to inhibit SARS-CoV replication.
authors.affiliation: Department of Biochemistry, University of Hong Kong, Pokfulam, Hong Kong.
authors.forename: Ka To
authors.initials: KT
authors.lastname: Shum
authors.forename: Julian A
authors.initials: JA
authors.lastname: Tanner
mesh_terms: D052157:Aptamers, Nucleotide / Q000737:chemistry / Q000494:pharmacology*; D001483:Base Sequence; D004265:DNA Helicases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054856:G-Quadruplexes; D020128:Inhibitory Concentration 50; D007700:Kinetics; D045473:Severe acute respiratory syndrome-related coronavirus / Q000201:enzymology*; D014764:Viral Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D052157:Aptamers, Nucleotide; D014764:Viral Proteins; D004265:DNA Helicases