 |
|
Title
|
|
Periplasmic disulphide bond formation is essential for cellulase secretion by the plant pathogen Erwinia chrysanthemi.
|
|
|
Authors
|
|
I.Bortoli-German,
E.Brun,
B.Py,
M.Chippaux,
F.Barras.
|
|
|
Ref.
|
|
Mol Microbiol, 1994,
11,
545-553.
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
Secretion to the cell exterior of cellulase EGZ and of at least six pectinases
enables the Gram-negative Erwinia chrysanthemi to cause severe plant disease.
The C-terminal cellulose-binding domain (CBD) of EGZ was found to contain a
disulphide bond which forms, in the periplasm, between residues Cys-325 and
Cys-382. Dithiothreitol (DTT)-treatment of native EGZ showed that the disulphide
bond was dispensable, both for catalysis and cellulose binding. Adding DTT to E.
chrysanthemi cultures led to immediate arrest of secretion of EGZ which
accumulated in the periplasm where the CBD was eventually proteolysed.
Site-directed mutagenesis that affected Cys residues involved in disulphide bond
formation resulted in molecules that were catalytically active and able to bind
to cellulose but were no longer secreted. Instead they accumulated in the
periplasm. Interestingly, the region around EGZ Cys-325 is conserved in two
pectinases secreted by the same pathway as EGZ. We conclude that the conserved
Cys, and possibly adjacent residues, bear essential information for EGZ to be
secreted and that periplasmic disulphide bond formation is an obligatory step
which provides a pre-folded functional form of EGZ with secretion competence.
|
|
|
|