BIOCHEMICAL-CHARACTERIZATION OF THE PECTATE LYASE PELZ OF ERWINIA-CHRYSANTHEMI-3937

To degrade the plant pectin, the phytopathogenic bacterium Erwinia chr ysanthemi 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 overproduc ed in E. coli and purified to compare its enzymatic properties to that of the other Pels of E. chrysanthemi. PelZ exhibits a low specific ac tivity but good affinity for the substrates including partially methyl ated pectins (up to 45% methylation). The main characteristic of PelZ is the requirement for both Ca2+ and Mn2+ as cofactors while the other Pels require only Ca2+. The cooperative effect of these two cations s uggests the presence of distinct binding sites. The PelZ activity is s ensitive to inhibition by excess of substrate, by oligogalacturonides, by the ionic strength and by different plant compounds. PelZ was show n to act in synergy with the major isoenzyme Pelf, while competition w as observed between PelZ and the minor pectate lyase Pelt. No synergis tic action was observed between PelZ and PelA, PelB, PelC or PelD. (C) 1998 Elsevier Science B.V.