Genetic determinants of receptor-binding preference and zoonotic potential of H9N2 avian influenza viruses

Abstract

16Receptor recognition and binding is the first step of viral infection and a key determinant of host 17 specificity. The inability of avian influenza viruses to effectively bind human-like sialylated receptors 18 is a major impediment to their efficient transmission in humans and pandemic capacity. Influenza 19H9N2 viruses are endemic in poultry across Asia and parts of Africa where they occasionally infect 20 humans and are therefore considered viruses with zoonotic potential. We previously described 21 H9N2 viruses, including several isolated from human zoonotic cases, showing a preference for 22human-like receptors. Here we take a mutagenesis approach, making viruses with single or multiple 23 substitutions in H9 haemagglutinin to determine the genetic basis of preferences for alternative 24 avian receptors and for human-like receptors. We describe amino acid motifs at positions 190, 226 25and 227 that play a major role in determining receptor specificity, and several other residues such 26as 159, 188, 193, 196, 198 and 225 play a smaller role. Furthermore, we show changes at residues 27 135, 137, 147, 157, 158, 184, 188, and 192 can also modulate virus receptor avidity and that 28 substitutions that increased or decreased the net positive charge around the haemagglutinin 29 receptor-binding site show increases and decreases in avidity, respectively. The motifs we identify 30 as increasing preference for the human-receptor will help guide future H9N2 surveillance efforts 31 and facilitate our understanding of the emergence of influenza viruses with high zoonotic potential. 32

Co-infection of chickens with H9N2 and H7N9 avian influenza viruses leads to emergence of reassortant H9N9 virus with increased fitness for poultry and enhanced zoonotic potential

“…The H9N2 and genotype 122 H9N9 viruses were found to have an optimal pH fusion of 5.4, which was slightly lower compared to that of Anhui/13 H7N9 having an optimal pH fusion 5.6 as seen previously (Chang et al, 2020). The results suggested that the reassortant H9N9 virus has a relatively more acid stable HA and stronger avidity for both human-like (6SLN) and avian-like (3SLN and 3SLN(6-su) receptors, thereby maintaining adaptation of such viruses for poultry while also enabling additional zoonotic potential (Peacock et al, 2020;Russier et al, 2016).…”

“…Thus, increased viral replication of reassortant viruses bearing the NA (N9) of Anhui/13 origin in human A549 cells and MDCK cells may be a consequence of the N9 enhancing the binding avidity to the human-like 6SLN receptors. Viruses with preferable binding towards 3SLN(6-su) may have an increased propensity for circulation in terrestrial poultry (Gambaryan et al, 2008;Peacock et al, 2020), and this observation was reflected in the successful generation and transmission of these H9N9 genotypes in chickens in our in vivo experiment. The H9N2 and genotype 122 H9N9 viruses were found to have an optimal pH fusion of 5.4, which was slightly lower compared to that of Anhui/13 H7N9 having an optimal pH fusion 5.6 as seen previously (Chang et al, 2020).…”

Evaluating the epizootic and zoonotic threat of an H7N9 low pathogenicity avian influenza virus (LPAIV) variant associated with enhanced pathogenicity in turkeys

“…The L217Q polymorphism has been previously shown, for various IAV strains including H7N9, to change the receptor preference by increasing the affinity of haemagglutinin to α-2,6 SA [12][13][14]. The A/Anhui/1/13 isolate being a human derived virus has a naturally high affinity to α2,6, but is also able to bind α-2,3 SA with a relatively high affinity [14,[39][40][41].…”

“…Amino acid position 217 is located in the 220-loop of the HA protein forming part of the influenza A virus receptor binding site. Possession of a L at position 217 has been previously shown to increase the affinity of HA binding to 'human-like', α-2,6 sialic acid (SA), while a Q at position 217 increases affinity of binding to 'avian-like', α2,3 SA [12][13][14]. Thus, the Q217L polymorphism present in wave 1-5 (2013-2017) H7N9 viruses, along with other molecular motifs such E627K in the basic polymerase 2 (PB2) protein, have been attributed to the zoonotic potential of these viruses [15,16].…”