Sk. Saha et al., A REGULATORY MECHANISM FOR THE BALANCED SYNTHESIS OF MEMBRANE PHOSPHOLIPID SPECIES IN ESCHERICHIA-COLI, Bioscience, biotechnology, and biochemistry, 60(1), 1996, pp. 111-116
The mechanism that assures the balanced synthesis of zwitterionic (pho
sphatidylethanolamine) and acidic phospholipids (phosphatidylglycerol
and cardiolipin) in Escherichia coli has been examined by genetically
manipulating the two enzymes at the biosynthetic branch point, i.e., p
hosphatidylglycerophosphate synthase, encoded by pgsA, and phosphatidy
lserine synthase, encoded by pssA. A mutant in which the most part of
the pssA gene was replaced with a drug resistance gene lacked phosphat
idylserine synthase and phosphatidylethanolamine and required divalent
metal ions for growth, as did a previously reported insertion-inactiv
ated pssA mutant. When this mutant harbored a plasmid containing a Bac
illus subtilis gene that encodes membrane-bound phosphatidylserine syn
thase, the phosphatidylethanolamine content was dependent on its activ
ity, in contrast to that with the soluble E. coli counterpart. A defec
tive mutation, pgsA3, caused reductions not only in acidic-phospholipi
d synthesis but also in phosphatidylethanolamine synthesis, despite th
e normal level of phosphatidylserine synthase activity. These results,
together with previous observations, indicate that phosphatidylserine
synthesis requires the membrane-associated form of phosphatidylserine
synthase, which is related to the membrane-levels of acidic phospholi
pids, thus yielding balanced compositions of zwitterionic and acidic p
hospholipids.