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RhlA diverts fatty acid biosynthetic intermediates to rhamnolipid formation
Author(s) -
Zhu Kun,
Rock Charles O.
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.643.6
Subject(s) - chemistry , rhamnolipid , biochemistry , fatty acid , biosynthesis , lysophospholipase , enzyme , pseudomonas aeruginosa , bacteria , biology , genetics , phospholipase
Pseudomonas aeruginosa secretes rhamnolipid (RL) that functions in hydrocarbon uptake, motility and pathogenesis. The acyl moieties in RL are derived from type II fatty acid synthesis (FASII), but how intermediates are diverted to RL is unclear. We show that RhlA is the first step in RL synthesis and competes with the dehydratases of FASII for the β‐hydroxyacyl‐ACP. Purified RhlA forms one molecule of β‐hydroxydecanoyl‐decanoate from two molecules of β‐hydroxydecanoyl‐ACP and is the only enzyme required to form the lipid component of RL. More than 95% of the acyl groups in RL are β‐hydroxydecanoyl, thus RhlA functions as a molecular ruler to selectively extract 10‐carbon intermediates. Eliminating either FabA or FabI activity increases RL production in P. aeruginosa showing that slowing FASII allows RhlA to more effectively compete for intermediate. In E. coli, the rate of fatty acid synthesis increases 30% when RhlA is expressed to ensure continued formation of fatty acids destined for phospholipid. Previous studies have placed a ketoreductase (RhlG) before RhlA in RL pathway, however, our genetic, biochemical and structural studies show that RhlG has no role in RL formation. We conclude that RhlA and RhlB are both necessary and sufficient for RL formation and the carbon flux through FASII accelerates to support RL production and maintain a supply of acyl chains for phospholipid. (supported by GM34496 and ALSAC)