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An NAD synthetic reaction bypasses the lipoate requirement for aerobic growth of E scherichia coli strains blocked in succinate catabolism
Author(s) -
Hermes Fatemah A.,
Cronan John E.
Publication year - 2014
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.12822
Subject(s) - biochemistry , coenzyme a , biology , lyase , glyoxylate cycle , isocitrate lyase , cofactor , escherichia coli , enzyme , reductase , gene
Summary The lipoate coenzyme is essential for function of the pyruvate ( PDH ) and 2‐oxoglutarate ( OGDH ) dehydrogenases and thus for aerobic growth of E scherichia coli . LipB catalyzes the first step in lipoate synthesis, transfer of an octanoyl moiety from the fatty acid synthetic intermediate, octanoyl‐ ACP , to PDH and OGDH . E . coli also encodes LplA , a ligase that in presence of exogenous octanoate (or lipoate) can bypass loss of LipB . LplA imparts Δ lipB strains with a ‘leaky’ growth phenotype on aerobic glucose minimal medium supplemented with succinate (which bypasses the OGDH ‐catalyzed reaction), because it scavenges an endogenous octanoate pool to activate PDH . Here we characterize a Δ lipB suppressor strain that did not require succinate supplementation, but did require succinyl‐ CoA ligase, confirming the presence of alternative source(s) of cytosolic succinate. We report that suppression requires inactivation of succinate dehydrogenase ( SDH ), which greatly reduces the cellular requirement for succinate. In the suppressor strain succinate is produced by three enzymes, any one of which will suffice in the absence of SDH . These three enzymes are: trace levels of OGDH , the isocitrate lyase of the glyoxylate shunt and an unanticipated source, aspartate oxidase, the enzyme catalyzing the first step of nicotinamide biosynthesis.