Table III.

Amino acid involved in substrate interaction and catalysis in GT-42 enzymes

CstI	CstII	HAC1267	HAC1268
Intermolecular contacts stabilizing the phosphate moiety of CMP in the Cst proteins
Asn46	Asn31	Asn33	Asn35
Tyr171	Tyr156	Tyr161	Gly166
Tyr177	Tyr162	His167	His172
Specific amino acids for bi-functional Cst-II variants
Asn66	Asn51	Asn53	Asn55
Val69	Leu54	Val56	Val58
Phe284	Ile269	Lys256	Ser242
Catalytic histidine
His202	His188	His184	His190
Acceptor
Galβ1-3/4R	Galβ1-3/4R	LacNAc>Lac	LacNAc>Lac
	Neu5Acα2-3Galβ1-3/4R	>>>Galβ1-3GlcNac (trace)	>>>Galβ1-3GlcNac (trace)
Linkage
Mono-functional α2-3-sialylated	Bi-functional α2-3/α2-8-sialylated	Mono-functional α2-3-sialylated	Mono-functional α2-6-sialylated