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This review is an attempt to bring together and critically evaluate the now-abundant but dispersed data concerning the lipid intermediates of the biosynthesis of bacterial peptidoglycan. Lipid I, lipid II, and their modified forms play a key role not only as the specific link between the intracellular synthesis of the peptidoglycan monomer unit and the extracytoplasmic polymerization reactions but also in the attachment of proteins to the bacterial cell wall and in the mechanisms of action of antibiotics with which they form specific complexes. The survey deals first with their detection, purification, structure, and preparation by chemical and enzymatic methods. The recent important advances in the study of transferases MraY and MurG, responsible for the formation of lipids I and II, are reported. Various modifications undergone by lipids I and II are described, especially those occurring in gram-positive organisms. The following section concerns the cellular location of the lipid intermediates and the translocation of lipid II across the cytoplasmic membrane. The great efforts made since 2000 in the study of the glycosyltransferases catalyzing the glycan chain formation with lipid II or analogues are analyzed in detail. Finally, examples of antibiotics forming complexes with the lipid intermediates are presented.

An unusual type of bacterial cell wall was encountered in a Bacillus strain referred to as Bacillus sp. C.I.P. 76-111, The major constituent of this cell wall is a high-molecular-weight anionic protein non-covalently associated to a peptidoglycan-polysaccharide complex. The cell wall appeared as a multilayered structure when sections of whole cells or of isolated cell walls fixed with glutaraldehyde and postfixed with osmium tetroxide were examined by electron microscopy. The correlation between the observed morphological features and the biochemical data suggested that a thin central electron-dense layer identifiable with the peptidoglycan-polysaccharide complex is located between two similar thick layers of protein. Furthermore, negative staining of isolated cell walls revealed that the outer protein layer has a regular surface array of subunits with hexagonal symmetry. Several structural properties of the cell wall peptidoglycan were investigated and were found to resemble those of other bacilli. Further characterization of the autolytic system showed that an N-acetylmuramyl-L-alanine amidase and a glycosidase, presumably a N-acetyl-muramidase, were associated with the peptidoglycan-polysaccharide complex. It was also established that this strain is devoid of membrane teichoic acid. [ABSTRACT FROM AUTHOR]