Figure 7.

Inhibition of SARS-CoV-2 exonuclease activity by velpatasvir for remdesivir (R) terminated RNA. A mixture of 500 nM RNAs (sequences shown in (a), (j)) and 50 nM SARS-CoV-2 pre-assembled exonuclease complex (nsp14/nsp10) was incubated in buffer solution at 37 °C for 15 min in the absence (b), (f), (k) or presence of varying amounts of velpatasvir (c-e), (l), elbasvir (g), daclatasvir (h) or ledipasvir (i). The intact RNAs (a), (j) and the products of the exonuclease reaction (b-i), (k-l) were analyzed by MALDI-TOF MS. The signal intensity in each graph was normalized to the highest peak. In (a-i) the peak at 8165 Da corresponds to the full-length RNA and in (j-l) the peak at 8209 Da corresponds to remdesivir (R)-terminated RNA. In the absence of velpatasvir or elbasvir, exonuclease activity caused nucleotide cleavage from the 3’-end of the RNA as shown by the lower molecular weight fragments corresponding to cleavage of 1–7 nucleotides (b), (f), (k). In the presence of velpatasvir, elbasvir, daclatasvir or ledipasvir, exonuclease activity was significantly reduced as shown by the reduced intensities of the fragmentation peaks and increased peak of the intact RNA (c-e), (g-i), (l).