Morphology of the peptidoglycan of Bacillus subtilis illustrating the cooperative complexation effect of a metal ion M with teichoic acid.
To protect themselves, bacteria possess within their membranes a kind of external skeleton made of a polymer, the peptidoglycan. Scientists of SCIB, together with IBS, the “centre d’ingénierie des protéines” of Liège and the Newcastle Institute of Biosciences, succeeded in the solid state NMR analysis of peptidoglycan obtained from different bacteria with an unprecedented resolution. The final purpose of the work: to better understand the role and functions of this important part of the bacterial membrane, the target of numerous antibiotics such as penicillin.
The bacterial membrane is a complex structure, differing from one species to the next. Its purpose is to protect and maintain the inner cohesion of this unicellular being, to manage the income of nutriments and the outcome of wastes, and to support communication with the outer world -- for instance, in the case of infection. Yet, there is one component common to all bacteria: the peptidoglycan. Moreover, it exists only in bacteria and is thus an ideal target for antibiotics. This polymer is made of chains of sugars linked together by peptides, short chains of amino acids. Its very large size required limiting the NMR study to only small models: monomers or freeze-dried peptidoglycans, which yields poor resolution spectra and only partial information.
Upon hydrating the peptidoglycan the scientists obtained, in spite of the huge size of the polymer, surprisingly perfectly resolved solid-state NMR spectra that allowed them to obtain a fine, more global study. Interesting discovery: the cellular membrane has the ability to complexify metal cations (Mg, Mn) under the cooperative effects of peptidoglycan and teichoic acids, other components of the cell wall made of long phosphorylated polymeric chains. The affinity is much larger than that of these two components as pure compounds.
Further reading: T. Kern et al., J. Amer. Chem. Soc. 132 (2010) 10911
Maj : 18/02/2014 (963)