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Applied and Environmental Microbiology, August 2001, p. 3603-3609, Vol. 67, No. 8
Mikrobiologie/Biotechnologie,
Eberhard-Karls-Universität Tübingen, D-72076
Tübingen, Germany
Received 31 January 2001/Accepted 7 May 2001
Streptomyces viridochromogenes Tü494 produces
the antibiotic phosphinothricin tripeptide (PTT). In the postulated
biosynthetic pathway, one reaction, the isomerization of
phosphinomethylmalate, resembles the aconitase reaction of the
tricarboxylic acid (TCA) cycle. It was speculated that this reaction is
carried out by the corresponding enzyme of the primary
metabolism (C. J. Thompson and H. Seto, p. 197-222,
in L. C. Vining and C. Stuttard, ed., Genetics and Biochemistry of Antibiotic Production,
1995). However, in addition to the TCA cycle aconitase gene, a gene
encoding an aconitase-like protein (the phosphinomethylmalate
isomerase gene, pmi) was identified in the PTT
biosynthetic gene cluster by Southern hybridization experiments, using
oligonucleotides which were derived from conserved amino acid sequences
of aconitases. The deduced protein revealed high similarity to
aconitases from plants, bacteria, and fungi and to iron regulatory
proteins from eucaryotes. Pmi and the S.
viridochromogenes TCA cycle aconitase, AcnA, have 52% identity. By gene insertion mutagenesis, a pmi mutant
(Mapra1) was generated. The mutant failed to produce PTT, indicating
the inability of AcnA to carry out the secondary-metabolism reaction. A
His-tagged protein (Hispmi*) was heterologously produced in Streptomyces lividans. The purified protein showed no
standard aconitase activity with citrate as a substrate, and the
corresponding gene was not able to complement an acnA
mutant. This indicates that Pmi and AcnA are highly specific for their
respective enzymatic reactions.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.8.3603-3609.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
The Phosphinomethylmalate Isomerase Gene
pmi, Encoding an Aconitase-Like Enzyme, Is Involved in
the Synthesis of Phosphinothricin Tripeptide in
Streptomyces viridochromogenes
*
Corresponding author. Mailing address:
Mikrobiologie/Biotechnologie, Eberhard-Karls-Universität
Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen,
Germany. Phone: 49 7071 29-74638. Fax: 49 7071 29-5979. E-mail:
schwartz{at}molbio.biol.biologie.uni-tuebingen.de.
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