Verlag des Forschungszentrums Jülich
JUEL-4203
Gande, Roland
Untersuchungen zur Lipid- und Zellwandsynthese in Corynebacterium glutamicum
128 S., 2006
Untersuchungen zur Lipid-und Zellwandsynthese in Corynebacterium glutamicum
Die Zellwand der Corynebacterianeae, zu denen unter anderem das
biotechnologisch genutzte Corynebacterium glutamicum gehört, besitzt neben der
Cytoplasmamembran eine zweite Lipiddoppelschicht die funktionell mit der auseren
Membran Gram negativer Bakterien vergleichbar ist. Beide Membranen sind
masgeblich am Stofftransport beteiligt. Diese Lipidmembranen bestehen aus
Fettsäuren und Mycolsäuren. Es war das Ziel dieser Arbeit die Synthese der
Mycolsäuren sowie die weiterer Zellwandbestandteile zu untersuchen.
Studies on the lipid and cell wall synthesis in Corynebacterium
glutamium
The Corynebacterianeae, such as Corynebacterium glutamicum or Mycobacterium
tuberculosis, possess unique and structurally diverse lipids, including the genus
specific mycolic acids. These α-branched, β-hydroxylated fatty acids form an outer
permeability barrier not present in other gram positive bacteria. Whereas the
chemical structure of mycolic acids is known, only recently details on its synthesis
also emerge. This work shows the involvement of several genes of C.glutamicum in
mycolic acid synthesis,transfer and translocation. The key player in this process is
obviously the highly conserved polyketide synthase (pks)showing strong homology
to the mycobacterial pks13. The corresponding gene product condenses two
preformed linear fatty acids to yield mature mycolic acids. Additionally the whole
chromosomal region adjacent to pks shows synteny in all Corynebacterianeae. The
present study on pks and the adjacent accD3,whose gene product resembles the β-
subunit of the acetyl-CoA carboxyltransferase in E.coli, revealed a complete loss of
mycolic acids in mutants inactivated in pks or accD3. Interestingly C.glutamicum
possesses four paralogous acyl-CoA carboxyltransferasesases. Isolation of His-
tagged AccD3 resulted in co-purification of AccD2, one of the carboxylase
paralogous together with AccBC which is the biotinylated α-subunit essential for
carbon dioxide fixation. Disruption of accD2 also led to a complete loss of mycolic
acids similar to the accD3 and pks inactivation mutant. Considering these results the
following model is suggested:The AccD2-AccD3-AccBC complex is involved in
carboxylating a linear fatty acid precursor similar to carboxylation of acetyl-CoA
required for linear fatty acid synthesis catalysed by the Fas system. The carboxylated
precursor is used by Pks to establish a Claisen-like condensation with a second
probably not activated fatty acid to yield mature mycolic acids which are transferred
into the cell wall to form an outer lipid bilayer similar to the outer membrane of gram
negative bacteria.
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