Characterization of recombinant rhamnogalacturonan alpha-L-rhamnopyranosyl-(1,4)-alpha-D-galactopyranosyluronide lyase from Aspergillus aculeatus - An enzyme that fragments rhamnogalacturonan I regions of pectin

The four major oligomeric reaction products from saponified modified hairy regions (MHR-S) from apple, produced by recombinant rhamnogalacturonan (RC) alpha-L-rhamnopyranosyl-(1,4)-alpha-D-galactopyranosyluronide lyase (rRG-lyase) from Aspergillus aculeatus, were isolated and characterized by H-1-nuclear magnetic resonance spectroscopy. They contain an alternating RC backbone with a degree of polymerization of 4, 6, 8, and 10 and with an alpha-Delta-(4,5)-unsaturated D-galactopyranosyluronic acid at the nonreducing end and an L-rhamnopyranose at the reducing end. L-Rhamnopyranose units are substituted at C-4 with beta-galactose. The maximum reaction rate of rRG-lyase toward MHR-S at pH 6.0 and 31 degrees C was 28 units mg(-1). rRG-lyase and RC-hydrolase cleave the same alternating RG I subunit in MHR. Both of these enzymes fragment MHR by a multiple attack mechanism. The catalytic efficiency of rRG-lyase for MHR increases with decreasing degree of acetylation. Removal of arabinose side chains improves the action of rRG-lyase toward MHR-S. In contrast, removal of galactose side chains decreased the catalytic efficiency of rRG-lyase. Native RG-lyase was purified from A. aculeatus, characterized, and found to be similar to the rRG-lyase expressed in Aspergillus oryzae.