TABLE 2.

Charged substituents of the classical lipid A^a

Species	Substituent at position 1	Substituent at position 4′	Formal net chargeb
Escherichia coli	PP	P	−4
Proteus mirabilis	P	PEtN	−1.5
Rhizobium meliloti	P	P	−3
Rhodobacter capsulatus	PPEtN	PEtN	−1
Rhodocyclus gelatinosus	PEtN	PPEtN	−1
Sphaerotilus natans	P	PPEtN	−2.5
Neisseria meningitidis	PPEtN	PPEtN	−2

^aFor references, see reference 735. Abbreviations: PP, pyrophosphate; P, phosphate; PEtN, phosphoethanolamine; PPEtN, pyrophosphoethanolamine.

^bFor simplicity, phosphomonoesters were assumed to have a 1.5 negative charge at neutral pH.