Table 2.

Receptor binding specificity, HA activation pH, and molecular markers of H1 influenza viruses.

Virus	Binding Specificity			Fusion pH			HA a				PB2							PB1-F2
	Sialic Acid	Source		pH	Source		190	225	226		271	588	590	591	627	701		66
1918	α2,6	[42,48]		5.1	[51]		D	D	Q		T	A	G	Q	K	D		S
NJ/08	α2,6/α2,3	[39,40,52]		5.5–5.6	[53]		D	G	Q		T	A	G	Q	K	D		N
MN/45	α2,6	[53]		5.5–5-6	[53]		D	G	Q		A	T	S	R	E	D		- b
TX/14	α2,6/α2,3	[40,53]		5.7	[53]		D	N	Q		A	T	S	R	E	D		N
OH/02	α2,6	[40,53]		5.6	[53]		D	D	Q		A	T	S	R	E	D		N
OH/09	α2,6/α2,3	[53]		5.7	[53]		D	G	Q		A	I	S	R	E	D		S
IA/39	α2,6	[53]		5.6–5.7	[53]		D	D	Q		A	T	S	R	E	D		N
CA/07	α2,6	[45,46]		5.5	[53]		D	D	Q		A	T	S	R	E	D		-
TX/15	α2,6/α2,3	[54]		5.4–5.5	[53]		D	D	Q		A	T	S	R	E	D		-
Bris/59	α2,6	[40]		5.3–5.4	[53]		D	D	Q		A	I	G	Q	K	D		N
MN/19	α2,6/α2,3	[53]		5.6–5.7	[53]		N	D	Q		A	T	S	R	E	D		N
WI/71	α2,6/α2,3	[53]		5.7	[53]		D	D	Q		S	T	S	R	E	D		N

^a H3 numbering. ^b Protein is truncated containing either 8 (MN/45) or 11 (CA/07 and TX/15) amino acids. IA/39 contains 79 amino acids. The full-length protein contains 90 amino acids.