Synopsis The Structure, Activity, and Function of Lipid

Synopsis The Structure, Activity, and Function of Lipid A 

As the preceding sections show, the term lipid A does not denote a defined molecular entity but rather a family of structurally closely related but not identical phosphoglycolipids. Their structures may differ in the type and number (one or two) of HexpN residues present in the backbone by the number, location, nature, size, and linkage of acyl residues by the nature of phosphate substituents and finally by the degree of phosphorylation of the backbone. Lipid A components of different bacterial origin are classified in the present article on the basis of structural variations. 

Lipid A having Kdo attached at 0-6 comprises a domain of LPS that exhibits a remarkable structural conservatism, as far as the principal architecture is concerned (Fig. 15). This type of structure is found in most Gramnegative bacteria. It is not present in other biomolecules and is thus unique to Gram-negative bacteria and their LPS. It contains those structures that are required for (/) bacterial viability and (//) for optimal expression of endotoxic activity. 

On the other hand, the negatively charged Kdo-lipid A domain constitutes a target for binding of certain antibiotics, such as polymyxin B (125) and basic peptides derived from host cells such as the bactericidal/perme-ability-increasing protein (BPI) (261). In this respect the Kdo-lipid A domain constitutes a weak site of the outer membrane, rendering bacteria vulnerable to the action of cationic agents. 

The financial support of the Deutsche Forschungs Gemeinschaft (SFB 367, project B2) and Fonds der Chemie (EThR) is greatly appreciated. We thank M. Lohs, F. Richter, B. Kdhler and 

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