Purification and characterization of two inducible exopolygalacturonases from Aspergillus kawachii

BYRNE, CRISTIAN; CAVALITTO, SEBASTIÁN FERNANDO; VOGET, CLAUDIO ENRIQUE

Biocatalysis and Agricultural Biotechnology

Elsevier

Lugar: Taichung; Año: 2017 vol. 10 p. 38 - 45

1878-8181

Of twoexopolygalacturonases purified and characterized from an Aspergillus kawachii culturegrown on lemon pomace, the main one, exoPG1, was a glycosylated protein with amolecular mass of 75 kDa, isoelectric point in the 4.00?4.65 pH range, and a 3.0?4.0 pH optimum, though with activity at pH 2.0. ExoPG1cleaved monomer units irrespective of the degree of substrate polymerization.Di- and trigalacturonic acids were completely hydrolyzed, whereaspolygalacturonic acid (PGA) only incompletely. ExoPG1, along with a recombinantendoPG from the same fungal strain, was necessary for the hydrolysis of PGAdown to the monomer. pH stability was maximum in the range 4.0?5.0irrespective of the incubation temperature and decreased as the temperatureincreased from 30 to 70 °C. The enzyme appeared not to require divalent cationsfor activity. Protein identification by MALDI-TOF-TOF MS/MS indicated homologyof exoPG1 with the exopolygalacturonase PGXB of Aspergillus. niger, anexopolygalacturonase of Aspergillus tubingensis, and the exopolygalacturonase Xof Aspergillus kawachii, a hypothetical enzyme predicted from the completesequencing of the genome of the fungus. Both these latter proteins are unusualin that they have identical primary sequences. We therefore conclude  that exoPG1 is probably the hypothetical A.kawachii exopolygalacturonase X. ExoPG2?having a molecular weight of 80 kDa, anisoelectricpoint between pHs 4.5 and 5.0, a 4.0 pH optimum, and kinetics withPGA similar to those of exoPG1?shared similarities with the exopolygalacturonase PGXCof A. niger and another proposed exopolygalacturonase of A. kawachii. Thisreport is the first concerning exopolygalacturonases from A. kawachii