Biochemical characterization of the pectate lyase PelZ of Erwinia chrysanthemi 3937

摘要

To degrade the plant pectin, the phytopathogenic bacterium Erwinia chrysanthemi produces a set of at least seven endo-pectate lyases (Pels). Five major (PelA, PelB, PelC, PelD and PelE) and two minor isoenzymes (PelL and PelZ) have been identified. PelZ is an extracellular enzyme secreted by the Out system. According to its amino acid sequence, the PelZ protein belongs to a new family. The PelZ protein was overproduced in E. coli and purified to compare its enzymatic properties to that of the other Pels of E. chrysanthemi. PelZ exhibits a low specific activity but good affinity for the substrates including partially methylated pectins (up to 45% methylation). The main characteristic of PelZ is the requirement for both Ca~(2+) and Mn~(2+) as cofactors while the other Pels require only Ca~(2+). The cooperative effect of these two cations suggests the presence of distinct binding sites. The PelZ activity is sensitive to inhibition by excess of substrate, by oligogalacturonides, by the ionic strength and by different plant compounds. PelZ was shown to act in synergy with the major isoenzyme PelE, while competition was observed between PelZ and the minor pectate lyase PelL. No synergistic action was observed between PelZ and PelA, PelB, PelC or PelD.