TABLE 2.

Key ligand interactions

Ligand/protein atom (resolution)	Protein/water atom	Distance
		α-Neu5Ac (0.97 Å)	Neu5Ac2en (1.5 Å)	Covalent intermediate (1.2 Å)
		Å	Å	Å
O-1A	Arg615-N-η2	2.91	2.86	2.75
	Arg555-N-η1	3.15	3.14	3.13
	Arg555-N-η2	3.11	3.09	3.18
	H2O			2.95
O-1B	Arg615-N-η1	2.92	2.89	2.89
	Arg266-N-η1	3.01	2.86	2.99
	Arg266-N-η2	3.02	2.99	2.91
	H2O			2.90
O-2	Asp291-O-δ2	2.57
	H2O (W1)	2.93
F-1	Arg266-N-η1			2.96
	Asp291-O-δ1			2.87
O-4	Arg285-N-η2	2.97	2.92	2.95
	Asp328-O-δ1	2.68	2.71	2.69
O-7	H2O (W1)	3.15	2.73
	H2O			2.71
	H2O			2.83
O-8	Tyr485-O	2.82	2.77	2.74
	H2O (W3)	2.79	2.74	2.78
O-9	Gln493-O-ε1	2.73	2.76	2.97
	H2O (W3)	3.06	3.13	2.99
	H2O		2.65	3.17
O-10	H2O	2.84	2.74	2.80
N-5	Asp328-O-δ2	2.86	2.88	2.83
C-1	Tyr655-O	2.82	2.87	2.36
C-2	Tyr655-O	2.96	2.64	1.41
Glu539-O-ε1	Tyr655-O	3.13	3.08	3.25
Glu539-O-ε2	Tyr655-O	2.62	2.67	2.78
Arg555-N-η1	Tyr655-O	2.91	2.90	2.97