Biophysical and Biochemical Studies on the Fine Structure of the Sacculi from Escherichia coli and Staphylococcus aureus
The general principles of the chemical structure of the bacterial sacculus and the basic conformational features of its building bricks, — oligosaccharide chains bearing peptide side chains for crosslinking — are well known for a long time (for review see e.g. Schleifer and Kandler, 1972; Labischinski et al., 1985). However, these data gave only rough ideas how the real giant macromolecule murein (synonym: peptidoglycan) is organized to fulfill its functions like protecting the bacterial cell against its own osmotic pressure, maintaining shape, yet allowing growth and division of the cell. For these purposes the sacculus must confer rigidity, flexibility and structural dynamics at the same time. Obviously, the topology of the peptides to be crosslinked plays an important role for constructing a covalently linked sacculus. The enzymes engaged in this job are anchored in the cytoplasmic membrane and should crosslink peptides only, if these come in close spatial contact. For this reason, the helical nature of the murein glycan chains, which forces consecutive peptides along a sugar strand to point approximately to the left, downward, right and upward, largely limits the theoretical constructions of stress bearing, covalently linked networks (topotypes, see Labischinski et al., 1985; Labischinski and Johannsen, 1986; Koch, 1991). To differentiate between the still large number of possible arrangements, experimental data are urgently needed, but difficult to obtain for large, low-ordered macromolecular assemblies like the murein sacculus. This report will focus on two of the few experimental approaches available — small angle neutron solution scattering and HPLC-techniques to study enzymatically produced murein degradation products -, which recently contributed to our knowledge on the architecture of the gram-negative sacculus and on the interrelationships between peptidoglycan crosslinking fine structure and β-lactam resistance in staphylococci, respectively.
KeywordsCell Separation Methicillin Resistance Cross Wall Cylindrical Wall Cell Wall Architecture
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