title: Low-temperature-induced structural changes in human lysozyme elucidated by three-dimensional NMR spectroscopy.
abstract: The three-dimensional solution structures of human lysozyme were determined at 35 and 4 degrees C using the heteronuclear multidimensional NMR spectroscopy, which were compared with each other to clarify the structural response of this enzyme to lowering of the temperature. Together with the data of the temperature dependence experiments of the lytic activity against Micrococcus luteus, we consider the implication of the observed structural change for the low-temperature-induced reduction of the activity of human lysozyme. The structures of human lysozyme determined at the two temperatures are found to be similar, both of which comprise four alpha-helices (A- to D-helices) and three antiparallel beta-strands (beta(1)-beta(3)), leading to the constructions of the alpha- and beta-domains as previously identified in the X-ray crystal structure. A significant structural change was observed for the "active site lobe" comprising the loop region connecting C- and D-helices and the following D-helix, which moves toward the active site cleft located between the alpha- and beta-domains so as to obstruct the cleft according to the temperature lowering. It further appeared that the total volume as well as the accessible surface area of human lysozyme decreases with lowering of the temperature, suggesting that the internal cavity of this enzyme shrinks under low temperature environment. Because in human lysozyme the region comprising the active site lobe is responsible for turnover of the enzymatic reaction against the substrate, the low-temperature-induced structural change of the active site lobe presumably controls the efficiency of the lytic activity under low temperatures.
authors.affiliation: Protein Structure Research Group, Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1, Tsukisamu-Higashi, Toyohira, Sapporo 062-8517, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kumeta
authors.forename: Ai
authors.initials: A
authors.lastname: Miura
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kobashigawa
authors.forename: Kazunori
authors.initials: K
authors.lastname: Miura
authors.forename: Chitoshi
authors.initials: C
authors.lastname: Oka
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Nemoto
authors.forename: Katsutoshi
authors.initials: K
authors.lastname: Nitta
authors.forename: Sakae
authors.initials: S
authors.lastname: Tsuda
mesh_terms: D000818:Animals; D001433:Bacteriolysis; D002247:Carbon Isotopes; D002417:Cattle; D002645:Chickens; D003080:Cold Temperature; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D006801:Humans; D016982:Micrococcus luteus / Q000201:enzymology; D008892:Milk / Q000201:enzymology; D008958:Models, Molecular; D009113:Muramidase / Q000737:chemistry*; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D017686:Oncorhynchus mykiss; D011487:Protein Conformation; D011522:Protons; D013816:Thermodynamics
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D011522:Protons; C421864:hen egg lysozyme; D009113:Muramidase