Low-Molecular-Weight Pectate Lyase from Streptomyces thermocarboxydus

An actinomycete producing pectate lyase (PL) isolated from soil was affiliated as Streptomyces thermocarboxydus by 16S rDNA analysis. S. thermocarboxydus PL I was purified to homogeneity by two steps of column chromatography from the culture filtrate. The molecular mass of the PL I was estimated to be 28 kDa by SDS-PAGE, and using electrospray ionization mass spectrometry, it was determined to be 23,897 Da, low-molecular-weight type. The amino acid sequence of the N-terminal 22 residues of PL I suggest that the enzyme is calcified into Family 3 of polysaccharide lyase. The optimum pH value was 9.0, and the thermal and the pH stabilities were stable up to 50°C and at a pH ranging from 6 to 10, respectively. The enzyme was designated an endo-type because of the detection of oligo-galacturonic acids (GalUAs) as products from the initial reaction. Although S. thermocarboxydus PL I had little action on highly esterified polygalacturonic acid methylglycoside, pectin for the PL I was a better substrate than polygalacturonate. For these three substrates, the PL I showed maximum activity with the addition of 0.6 mM Ca2+. S. thermocarboxydus PL I acted on poly- and oligo-GalUAs over di-GalUA and better on the larger GalUAs until at least DP 8. The final products with the PL I were both 4,5-unsaturated di- and tri-GalUA. This is the first report of PL from S. thermocarboxydus.