Purification, partial amino acid sequence and structure of the product of raucaffricine-O-beta-D-glucosidase from plant cell cultures of Rauwolfia serpentina.

Plant cell suspension cultures of Rauwolfia produce within 1 week approximately 250 nkat/l of raucaffricine-O-beta-D-glucosidase. A five step procedure using anion exchange chromatography, chromatography on hydroxylapatite, gel filtration and FPLC-chromatography on Mono Q and Mono P delivered in a yield of 0.9% approximately 1200-fold enriched glucosidase. A short protocol employing DEAE sepharose, TSK 55 S gel chromatography and purification on Mono Q gave a 5% recovery of glucosidase which was 340-fold enriched. SDS-PAGE showed a Mr for the enzyme of 61 kDa. The enzyme is not glycosylated. Structural investigation of the enzyme product, vomilenine, demonstrated that the alkaloid exists in aqueous solutions in an equilibrium of 21(R)- and 21(S)-vomilenine in a ratio of 3.4:1. Proteolysis of the pure enzyme with endoproteinase Lys C revealed six peptide fragments with 6-24 amino acids which were sequenced. The two largest fragments showed sequences, of which the motif Val-Thr-Glu-Asn-Gly is typical for beta-glucosidases. Sequence alignment of these fragments demonstrated high homologies to linamarase from Manihot esculenta (81% identity) or to beta-glucosidase from Prunus avium (79% identity). Raucaffricine-O-beta-D-glucosidase seems to be a new member of the family 1 of glycosyl hydrolases.