Journal of Bacteriology, July 1999, p. 3912-3919, Vol. 181, No. 13
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Laboratoire de Génétique Moléculaire des Microorganismes et des Interactions Cellulaires, UMR-CNRS 5577, INSA, F-69621 Villeurbanne Cedex, France
Received 19 January 1999/Accepted 29 April 1999
Erwinia chrysanthemi 3937 secretes into the external
medium several pectinolytic enzymes, among which are eight isoenzymes of the endo-cleaving pectate lyases: PelA, PelB, PelC, PelD, and PelE
(family 1); PelI (family 4); PelL (family 3); and PelZ (family 5). In
addition, one exo-cleaving pectate lyase, PelX (family 3), has been
found in the periplasm of E. chrysanthemi. The E. chrysanthemi 3937 gene kdgC has been shown to exhibit
a high degree of similarity to the genes pelY of
Yersinia pseudotuberculosis and pelB of
Erwinia carotovora, which encode family 2 pectate lyases.
However, no pectinolytic activity has been assigned to the KdgC
protein. After verification of the corresponding nucleotide sequence,
we cloned a longer DNA fragment and showed that this gene encodes a
553-amino-acid protein exhibiting an exo-cleaving pectate lyase
activity. Thus, the kdgC gene was renamed pelW. PelW catalyzes the formation of unsaturated digalacturonates from polygalacturonate or short oligogalacturonates. PelW is located in the
bacterial cytoplasm. In this compartment, PelW action could complete
the degradation of pectic oligomers that was initiated by the
extracellular or periplasmic pectinases and precede the action of the
cytoplasmic oligogalacturonate lyase, Ogl. Both cytoplasmic pectinases,
PelW and Ogl, seem to act in sequence during oligogalacturonate
depolymerization, since oligomers longer than dimers are very poor
substrates for Ogl but are good substrates for PelW. The estimated
number of binding subsites for PelW is three, extending from subsite
2 to +1, while it is probably two for Ogl, extending from subsite
1
to +1. The activities of the two cytoplasmic lyases, PelW and Ogl, are
dependent on the presence of divalent cations, since both enzymes are
inhibited by EDTA. In contrast to the extracellular pectate lyases,
Ca2+ is unable to restore the activity of PelW or Ogl,
while several other cations, including Co2+,
Mn2+, and Ni2+, can activate both cytoplasmic lyases.
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