title: Characterization and evolution of a myrosinase from the cabbage aphid Brevicoryne brassicae.
abstract: The aphid myrosinase gene has been elucidated using Rapid Amplification of cDNA Ends-PCR. Sequencing has shown that aphid myrosinase has significant sequence similarity (35%) to plant myrosinases and other members of glycosyl hydrolase family 1 (GHF1). The residues acting as proton donor and nucleophile, in the hydrolysis of glucosinolates by aphid myrosinase, are identified as Glu 167 and Glu 374 respectively. The equivalent residues in plant myrosinase are Gln 187 and Glu 409 and for the cyanogenic beta-glucosidase Glu 183 and Glu 397. Thus it would appear that the absence of a proton donor is not necessary for the hydrolysis of glucosinolates as was thought to be the case for the plant myrosinases. Aphid myrosinase appears to be more similar to animal beta-O-glucosidases than to plant myrosinases, as assessed by sequence similarity and phylogenetic techniques. These results strongly suggest that myrosinase activity has twice arisen from beta-O-glucosidases in plants and animals. Comparison of aphid myrosinase with plant myrosinase has highlighted Lys 173 and Arg 312 as possibly playing a crucial role in the hydrolysis of glucosinolates by aphid myrosinase.
authors.affiliation: Department of Biology, Imperial College at Wye, University of London, Kent TN25 5AH, Wye, UK.
authors.forename: A M E
authors.initials: AM
authors.lastname: Jones
authors.forename: P
authors.initials: P
authors.lastname: Winge
authors.forename: A M
authors.initials: AM
authors.lastname: Bones
authors.forename: R
authors.initials: R
authors.lastname: Cole
authors.forename: J T
authors.initials: JT
authors.lastname: Rossiter
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001042:Aphids / Q000201:enzymology*; D001483:Base Sequence; D018076:DNA, Complementary / Q000032:analysis; D019143:Evolution, Molecular; D006026:Glycoside Hydrolases / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D017422:Sequence Analysis, DNA
chemical_list: D018076:DNA, Complementary; D006026:Glycoside Hydrolases; C022739:thioglucosidase