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J. Bacteriol., 02 1997, 697-704, Vol 179, No. 3
D Thibaut, D Bisch, N Ratet, L Maton, M Couder, L Debussche and F Blanche
Several assays of pristinamycin I synthetases based on adenylate or
thioester formation were developed. Purification to near homogeneity of
these enzymatic activities from cell extracts of Streptomyces
pristinaespiralis showed that three enzymes could activate all
pristinamycin I precursors. SnbA, a 3-hydroxypicolinic acid: AMP ligase
activating the first pristinamycin I residue, was purified 200-fold, using
an ATP-pyrophosphate exchange assay. This enzyme was shown to be a monomer
with an Mr of 67,000 as estimated by sodium dodecyl sulfate- polyacrylamide
gel electrophoresis. Then a multifunctional enzyme, consisting of two
identical subunits (SnbC) with Mrs of 240,000 and able to bind covalently
L-threonine as a thioester, was purified 100- fold. This protein also
activated L-aminobutyric acid, which is further epimerized to generate the
third residue of the pristinamycin I macrocycle. A third protein,
consisting of two identical subunits (SnbD) with Mrs estimated to be
between 250,000 and 350,000, was purified 200-fold. This large enzyme
catalyzed thioesterification and subsequent N-methylation of
4-dimethylamino-L-phenylalanine, the fifth pristinamycin I residue. SnbD
could also activate L-proline, the fourth pristinamycin I residue, and some
preparations retained a low but significant activity for the last two
pristinamycin I precursors. Finally, a single polypeptide chain (SnbE) with
an Mr of 170,000, catalyzing L-phenylglycine-dependent ATP-pyrophosphate
exchange, was purified 3,000-fold and characterized. Stepwise Edman
degradation of the entire polypeptides or some of their internal fragments
provided amino acid sequences for the four isolated proteins. The purified
SnbE protein was further shown to be a proteolytic fragment of SnbD.
Copyright © 1997, American Society for Microbiology
Purification of peptide synthetases involved in pristinamycin I biosynthesis
Departement Analyse, Centre de Recherche de Vitry-Alfortville, Rhone- Poulenc Rorer S.A., Vitry-sur-Seine, France.
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