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MPI für Biochemie  

Molecular Structural Biology
Wolfgang Baumeister

Mycobacteria

 

Outer Membrane of Mycobacteria and Corynebacteria

Mbovis_SC_TOM_web
The mycobacterial outer membrane (MOM) is physiologically equivalent to the outer membrane of Gram-negative bacteria but does not contain lipopolysaccharides. The bilayer of the outer membrane in mycobacteria and corynebacteria consists of covalently bound mycolic acids that form the inner leaflet and extractable lipids that are mainly, but probably not exclusively, located in the outer leaflet. The bilayer is only marginally thicker than that of the cell membrane (CM, ≈ 7nm) as cryo-electron tomography (TOM)  revealed. The membrane structure is also visible in ultrathin cryosection (CS) together with the domain-rich periplasmic layers of the peptidoglycan-arabinogalactan polymer. The periplasm, i.e. the space between the cell membrane and the outer membrane, has a thickness of about 30 nm.

Mycobacterial Porin

MspA_Ketten_1_web
The porin MspA of Mycobacterium smegmatis is a homooctamer and a remarkably heat-resistant and stable protein located in the mycobacterial outer membrane. Isolated MspA exhibits a hydrophobic outer surface and forms typical aggregates in solution. One characteristic assembly is a zipper-like arrangement indicating the hight of the hydrophobic area in the electron microscope. The hydrophobic zone is clearly less than 7 nm in agreement with the total thickness of the outer membrane. A considerable large portion of the porin is exposed to the outer surface and can be identified in micrographs of isolated cell wall patches.

 

Selected Publications

  1. C. Hoffmann, A. Leis, M. Niederweis, J. Plitzko, H. Engelhardt (2008) Disclosure of the mycobacterial outer membrane: Cryo-electron tomography and vitreous sections reveal the lipid bilayer structure. Proc. Natl. Acad. Sci. USA 105: 3963-3967
  2. C. Heinz, H. Engelhardt, M. Niederweis (2003) The core of the tetrameric mycbacterial porin MspA is an extremely stable beta-sheet domain. J. Biol. Chem. 278: 8678-8685
  3. H. Engelhardt, M. Niederweis (2002) A tetrameric porin limits the cell wall permeability of Mycobacterium smegmatis. J. Biol. Chem. 277: 37567-37572