Synergism between Erwinia pectate lyase isoenzymes that depolymerize both pectate and pectin

Area of Science:

• Microbiology
• Plant Pathology
• Enzymology

Background:

• Phytopathogenic Erwinia bacteria cause plant tissue maceration via pectinolytic enzymes, notably pectate lyase (PL).
• Understanding the genetic organization and function of PL isoenzymes is crucial for comprehending Erwinia pathogenicity.

Purpose of the Study:

• To investigate the genomic organization of PL isoenzymes in Erwinia carotovora subsp. atroseptica.
• To characterize the kinetic properties and substrate specificities of individual and combined PL isoenzymes.
• To explore potential synergistic interactions among PL isoenzymes in degrading different pectin substrates.

Main Methods:

• Sequencing of a 7.5 kbp genomic region encoding three PL isoenzyme genes.
• Expression of pel genes in Escherichia coli-pT7-7 system and purification of recombinant PLs.
• Determination of kinetic properties and degradation assays using pectate and pectin substrates with varying esterification levels.

Main Results:

• The study identified three PL isoenzyme genes with conserved promoter regions homologous to the KdgR repressor binding site.
• Recombinant PL isoenzymes (PL1, PL2, PL3) were purified with high yield and purity, exhibiting distinct kinetic properties.
• Individual PL isoenzymes preferentially degraded 31% esterified pectin over pectate; combinations with PL3 significantly enhanced degradation of 68% esterified pectin.

Conclusions:

• The PL isoenzymes of Erwinia carotovora subsp. atroseptica exhibit substrate specificity and potential for synergistic activity.
• Combinatorial action of PL isoenzymes broadens the range of pectic substrates degradable by the bacterium, contributing to pathogenicity.