title: "Newton's cradle" proton relay with amide-imidic acid tautomerization in inverting cellulase visualized by neutron crystallography.
abstract: Hydrolysis of carbohydrates is a major bioreaction in nature, catalyzed by glycoside hydrolases (GHs). We used neutron diffraction and high-resolution x-ray diffraction analyses to investigate the hydrogen bond network in inverting cellulase PcCel45A, which is an endoglucanase belonging to subfamily C of GH family 45, isolated from the basidiomycete Phanerochaete chrysosporium. Examination of the enzyme and enzyme-ligand structures indicates a key role of multiple tautomerizations of asparagine residues and peptide bonds, which are finally connected to the other catalytic residue via typical side-chain hydrogen bonds, in forming the "Newton's cradle"-like proton relay pathway of the catalytic cycle. Amide-imidic acid tautomerization of asparagine has not been taken into account in recent molecular dynamics simulations of not only cellulases but also general enzyme catalysis, and it may be necessary to reconsider our interpretation of many enzymatic reactions.
authors.affiliation: Department of Biomaterials Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Nakamura
authors.affiliation: Department of Biomaterials Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Ishida
authors.affiliation: Frontier Research Center for Applied Atomic Sciences, Ibaraki University, Ibaraki 319-1106, Japan.
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Kusaka
authors.affiliation: Frontier Research Center for Applied Atomic Sciences, Ibaraki University, Ibaraki 319-1106, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Yamada
authors.affiliation: Department of Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Fushinobu
authors.affiliation: Frontier Research Center for Applied Atomic Sciences, Ibaraki University, Ibaraki 319-1106, Japan.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Tanaka
authors.affiliation: Department of Subtropical Biochemistry and Biotechnology, Faculty of Agriculture, University of the Ryukyus, Okinawa 903-0213, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kaneko
authors.affiliation: Japanese Experiment Module (JEM) Utilization Center, Japan Aerospace Exploration Agency, Ibaraki 305-8505, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Ohta
authors.affiliation: Confocal Science Inc., Tokyo 101-0032, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Tanaka
authors.affiliation: Maruwa Foods and Biosciences Inc., Nara 639-1123, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Inaka
authors.affiliation: Department of Life Science, University of Hyogo, Hyogo 678-1297, Japan.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Higuchi
authors.affiliation: Frontier Research Center for Applied Atomic Sciences, Ibaraki University, Ibaraki 319-1106, Japan.
authors.forename: Nobuo
authors.initials: N
authors.lastname: Niimura
authors.affiliation: Department of Biomaterials Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Samejima
authors.affiliation: Department of Biomaterials Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors.forename: Kiyohiko
authors.initials: K
authors.lastname: Igarashi
keywords: Carbohydrate Active enZymes; Cellulase; Neutron crystallography; Phanerochaete chrysosporium; Proton relay; Tautomerization; biomass