Synergistic hydrolysis of carboxymethyl cellulose and acid-swollen cellulose by two endoglucanases (CelZ and CelY) from Erwinia chrysanthemi

Erwinia chrysanthemi produces a battery of hydrolases and lyases which are very effective in the maceration of plant cell walls. Although two endogluc anases (CelZ and CelY; formerly EGZ and EGY) are produced, CelZ represents approximately 95% of thf total carboxymethyl cellulase activity. In this st udy, we have examined the effectiveness of CelY and CelZ alone and of combi nations of both enzymes using carboxymethyl cellulose (CMC) and amorphous c ellulose (acid-swollen cellulose) as substrates, Synergy was observed with both substrates. Maximal synergy (1.8-fold) was observed for combinations c ontaining primarily CelZ; the ratio of enzyme activities produced was simil ar to those produced by cultures of E. chrysanthemi. CelY and CelZ were qui te different in substrate preference. CelY was unable to hydrolyze soluble cellooligosaccharides (cellotetraose and cellopentaose) but hydrolyzed CMC to fragments averaging 10.7 glucosyl units. In contrast, CelZ readily hydro lyzed cellotetraose, cellopentaose, and amorphous cellulose to produce cell obiose and cellotriose as dominant products. CelZ hydrolyzed CMC to fragmen ts averaging 3.6 glucosyl units. In combination, CelZ and CelY hydrolyzed C MC to products averaging 2.3 glucosyl units. Synergy did not require the si multaneous presence of both enzymes. Enzymatic modification of the substrat e by CelY increased the rate and extent of hydrolysis by CelZ. Full synergy was retained by the sequential hydrolysis of CMC, provided CelY was used a s the first enzyme. A general mechanism is proposed to explain the synergy between these two enzymes based primarily on differences in substrate prefe rence.