title: Site-directed mutagenesis of possible catalytic residues of cellobiose 2-epimerase from Ruminococcus albus.
abstract: The cellobiose 2-epimerase from Ruminococcus albus (RaCE) catalyzes the epimerization of cellobiose and lactose to 4-O-beta-D-glucopyranosyl-D-mannose and 4-O-beta-D-galactopyranosyl-D-mannose (epilactose). Based on the sequence alignment with N-acetyl-D-glucosamine 2-epimerases of known structure and on a homology-modeled structure of RaCE, we performed site-directed mutagenesis of possible catalytic residues in the enzyme, and the mutants were expressed in Escherichia coli cells. We found that R52, H243, E246, W249, W304, E308, and H374 were absolutely required for the activity of RaCE. F114 and W303 also contributed to catalysis. These residues protruded into the active-site cleft in the model (alpha/alpha)(6) core barrel structure.
authors.affiliation: Laboratory of Biochemistry, Research Faculty of Agriculture, Hokkaido University, N-9 W-9, Kita-ku, Sapporo, 060-8589, Japan.
authors.forename: Shigeaki
authors.initials: S
authors.lastname: Ito
authors.forename: Shigeki
authors.initials: S
authors.lastname: Hamada
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ito
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Matsui
authors.forename: Tadahiro
authors.initials: T
authors.lastname: Ozawa
authors.forename: Hidenori
authors.initials: H
authors.lastname: Taguchi
authors.forename: Susumu
authors.initials: S
authors.lastname: Ito