The oligogalacturonate-specific porin KdgM of Erwinia chrysanthemi belongs to a new porin family.
The phytopathogenic Gram-negative bacteria Erwinia chrysanthemi secretes pectinases, which are able to degrade the pectic polymers of plant cell walls, and uses the degradation products as a carbon source for growth. We characterized a major outer membrane protein, KdgM, whose synthesis is strongly induced in the presence of pectic derivatives. The corresponding gene was characterized. Analysis of transcriptional fusions showed that the kdgM expression is controlled by the general repressor of pectinolytic genes, KdgR, by the repressor of hexuronate catabolism genes, ExuR, by the pectinase gene repressor, PecS, and by catabolite repression via the cyclic AMP receptor protein (CRP) transcriptional activator. A kdgM mutant is unable to grow on oligogalacturonides longer than trimers, and its virulence is affected. Electrophysiological experiments with planar lipid bilayers showed that KdgM behaves like a voltage-dependent porin that is slightly selective for anions and that exhibits fast block in the presence of trigalacturonate. In contrast to most porins, KdgM seems to be monomeric. KdgM has no homology with currently known porins, but proteins similar to KdgM are present in several bacteria. Therefore, these proteins might constitute a new family of porin channels.
Blot
Nicolas
N
Unité de Microbiologie et Génétique, Composante INSA, UMR-CNRS 5122, INSA, Bâtiment Louis Pasteur, 11 Avenue Jean Capelle, 69621 Villeurbanne Cedex, France.
Berrier
Catherine
C
Hugouvieux-Cotte-Pattat
Nicole
N
Ghazi
Alexandre
A
Condemine
Guy
G
D001483:Base Sequence; D002462:Cell Membrane / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology; D016974:Dickeya chrysanthemi / Q000737:chemistry*; D004591:Electrophoresis, Polyacrylamide Gel; D004594:Electrophysiology; D006603:Hexuronic Acids / Q000494:pharmacology; D008564:Membrane Potentials; D008954:Models, Biological; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D010368:Pectins / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011133:Polysaccharide-Lyases / Q000378:metabolism; D018272:Porins / Q000096:biosynthesis* / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D021381:Protein Transport; D013997:Time Factors; D014158:Transcription, Genetic
D003432:Cross-Linking Reagents; D006603:Hexuronic Acids; D018272:Porins; C007819:galacturonic acid; D010368:Pectins; D011133:Polysaccharide-Lyases; C023911:pectate lyase