title: Mapping protein matrix cavities in human cytoglobin through Xe atom binding.
abstract: Cytoglobin is the fourth recognized globin type, almost ubiquitously distributed in human tissues; its function is still poorly understood. Cytoglobin displays a core region of about 150 residues, structurally related to hemoglobin and myoglobin, and two extra segments, about 20 residues each, at the N- and C-termini. The core region hosts a large apolar cavity, held to provide a ligand diffusion pathway to/from the heme, and/or ligand temporary docking sites. Here we report the crystal structure (2.4A resolution, R-factor 19.1%) of a human cytoglobin mutant bearing the CysB2(38) --> Ser and CysE9(83) --> Ser substitutions (CYGB*), treated under pressurized xenon. Three Xe atoms bind to the heme distal site region of CYGB* mapping the protein matrix apolar cavity. Despite the conserved globin fold, the cavity found in CYGB* is structured differently from those recognized to play a functional role in myoglobin, neuroglobin, truncated hemoglobins, and Cerebratulus lacteus mini-hemoglobin.
authors.affiliation: Department of Physics-INFM and Centre for Excellence in Biomedical Research, University of Genova, Via Dodecaneso 33, Genoa I-16146, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: de Sanctis
authors.forename: Sylvia
authors.initials: S
authors.lastname: Dewilde
authors.forename: Alessandra
authors.initials: A
authors.lastname: Pesce
authors.forename: Luc
authors.initials: L
authors.lastname: Moens
authors.forename: Paolo
authors.initials: P
authors.lastname: Ascenzi
authors.forename: Thomas
authors.initials: T
authors.lastname: Hankeln
authors.forename: Thorsten
authors.initials: T
authors.lastname: Burmester
authors.forename: Martino
authors.initials: M
authors.lastname: Bolognesi
mesh_terms: D001665:Binding Sites; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D000078842:Cytoglobin; D005914:Globins; D006418:Heme / Q000737:chemistry*; D006801:Humans; D046911:Macromolecular Substances; D008958:Models, Molecular; D010544:Peroxidases / Q000737:chemistry*; D016062:Porosity; D011485:Protein Binding; D011487:Protein Conformation; D014978:Xenon / Q000737:chemistry*
chemical_list: C000627265:CYGB protein, human; D000078842:Cytoglobin; D046911:Macromolecular Substances; D014978:Xenon; D006418:Heme; D005914:Globins; D010544:Peroxidases