Table 1.

Enzymes involved in the structural modification of Kdo₂-lipid A in certain Gram-negative bacteria. The structure and numbering scheme for Kdo₂-lipid A is shown in Fig. 2

Positions	Enzymes	Function
1	LpxE	Removes the phosphate group from the 1-position of lipid A (Wang et al., 2004).
1	LpxT	Transfers a phosphate group to the 1-phosphate of lipid A (Touze et al., 2008).
1	LpxQ	Oxidizes the proximal glucosamine of lipid A to form an aminogluconate unit (Que-Gewirth et al., 2003).
1	LmtA	Catalyses the methylation of 1-phosphate of lipid A (Hinckley et al., 2005).
1	PmrC	Adds a phosphoethanolamine to the 1-position of lipid A (Lee et al., 2003).
1 or 4′	ArnT	Transfers an l-Ara4N unit to lipid A (Trent et al., 2001a,b,).
1 or 4′	EptC	Adds a phosphoethanolamine to the flagellar rod protein and the 1 or 4′ position of lipid A (Cullen et al., 2012).
2	PagP	Transfers a palmitate to the 2-position of lipid A (Hwang et al., 2004; Bishop, 2008).
2 or 2′	LpxD2	Adds a shorter 3-OH fatty acid group to 2- or 2′-position of lipid A at low temperature (Li et al., 2012).
2′	LpxP	Incorporates a palmitoleoyl moiety in place of the secondary laurate chain (Vorachek-Warren et al., 2002).
2′	LpxXL	Incorporates a very long fatty acid chain in place of the secondary laurate chain (Basu et al., 2002).
3	PagL	Removes the 3-O-linked acyl chain of lipid A (Rutten et al., 2006).
3′	LpxO	Adds an OH group to the αβ3′-position (Gibbons et al., 2000, 2008).
3′	AlmG	Adds glycine or diglycine residues to the αβ3′-position (Hankins et al., 2012)
3′	LpxR	Removes the 3′-acyloxyacyl moiety (Reynolds et al., 2006).
4′	LpxF	Removes the phosphate group from the 4′-position of lipid A (Wang et al., 2006).
Kdo	RgtA	Adds a GalA moiety to the distal unit of Kdo (Kanjilal-Kolar et al., 2006).
Kdo	RgtB	Adds a GalA moiety to the distal unit of Kdo (Kanjilal-Kolar et al., 2006).
Kdo	EptB	Adds a phosphoethanolamine to the distal unit of Kdo (Reynolds et al., 2005).
Kdo	KdoH1/KdoH2	Remove the distal unit of Kdo (Zhao & Raetz, 2010)