Saturday, March 11, 2006

Proposal for how the TolC channel passes through murein layer.


Artistic impression of purple TolC channel protein penetrating pores of peptidoglycan.


Just two days ago a proposed structure for the murein cell wall polymer was first reported.

In this paper there are wonderful colour images showing how the TolC "drainpipe" will just fit though proposed small pores in murein sheets. Another piece of the detailed stuctural reconstruction of bacterial surfaces just fell into place.


Three-dimensional structure of the bacterial cell wall peptidoglycan

The 3D structure of the bacterial peptidoglycan, the major constituent of the cell wall, is one of the most important, yet still unsolved, structural problems in biochemistry. The peptidoglycan comprises alternating N-acetylglucosamine (NAG) and N-acetylmuramic disaccharide (NAM) saccharides, the latter of which has a peptide stem. Adjacent peptide stems are cross-linked by the transpeptidase enzymes of cell wall biosynthesis to provide the cell wall polymer with the structural integrity required by the bacterium. The cell wall and its biosynthetic enzymes are targets of antibiotics. The 3D structure of the cell wall has been elusive because of its complexity and the lack of pure samples.

Herein we report the 3D solution structure as determined by NMR of the 2-kDa NAG-NAM(pentapeptide)-NAG-NAM(pentapeptide) synthetic fragment of the cell wall. The glycan backbone of this peptidoglycan forms a right-handed helix with a periodicity of three for the NAG-NAM repeat (per turn of the helix). The first two amino acids of the pentapeptide adopt a limited number of conformations. Based on this structure a model for the bacterial cell wall is proposed.

Samy O. Meroueh, Krisztina Z. Bencze, Dusan Hesek, Mijoon Lee, Jed F. Fisher, Timothy L. Stemmler, and Shahriar Mobashery
Three-dimensional structure of the bacterial cell wall peptidoglycan
PNAS published March 9, 2006, 10.1073/pnas.0510182103

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