Although conformational changes are essential for the function of proteins, little is known about their structural dynamics at atomic level resolution. Myoglobin (Mb) is the paradigm to investigate conformational dynamics because it is a simple globular heme protein displaying a photosensitivity of the iron-ligand bond. Upon laser photodissociation of carboxymyoglobin Mb a nonequilibrium population of protein structures is generated that relaxes over a broad time range extending from picoseconds to milliseconds. This process is associated with migration of the ligand to cavities in the matrix and with a reduction in the geminate rebinding rate by several orders of magnitude. Here we report nanosecond time-resolved Laue diffraction data to 1.55-Å resolution on a Mb mutant, which depicts the sequence of structural events associated with this extended relaxation. Motions of the distal E-helix, including the mutated residue Gln-64(E7), and of the CD-turn are found to lag significantly (100 -300 ns) behind local rearrangements around the heme such as heme tilting, iron motion out of the heme plane, and swinging of the mutated residue Tyr-29(B10), all of which occur promptly (<3 ns). Over the same delayed time range, CO is observed to migrate from a cavity distal to the heme known to bind xenon (called Xe4) to another such cavity proximal to the heme (Xe1). We propose that the extended relaxation of the globin moiety reflects reequilibration among conformational substates known to play an essential role in controlling protein function.myoglobin ͉ protein dynamics ͉ conformational states ͉ functional intermediates ͉ protein crystallography C onformational relaxations in proteins are characterized by a unique and very complex time-dependent structure. In myoglobin (Mb), reequilibration between conformational substates extends over at least six orders of magnitude in time, from picoseconds to nanoseconds (1). In parallel, functional properties respond with a drop in ligand binding reactivity of Ͼ1,000-fold, as established by transient laser spectroscopy (2,3). This is the manifestation of the existence and the role of a myriad of conformational substates that interconnect over the complex and rugged energy landscape of a protein (4, 5). Internal fluctuations are thought to permit interchange between conformational substates, thereby accounting for variations in substrate accessibility to the active site, ligand migration through the protein matrix, and ligand recombination after transient trapping within the protein. The structural basis of this extended conformational relaxation is, however, still largely unknown. We report an experiment by time-resolved Laue crystallography that unveils aspects of the complex time dependence of the structure of Mb and shows unexpected structural dynamics associated with the extended relaxation of the protein as observed in a large ensemble of molecules.Investigations of internal fluctuations have often been carried out on heme proteins, because of the possibility to rapidly photodissoc...

Inhaltsübersicht. Bislang kennt man das Auftreten von sowohl trigonal-planar als auch tetraedrisch koordiniertem Bor in einer Kristallstruktur nur aus der Bor-Sauerstoff-Chemie. Mit dem neuen Bariummetathioborat BaB 2 S 4 stellen wir nun zum erstenmal eine Verbindung vor, deren Anionenstruktur aus zu Ketten kondensierten BS 3 -und BS 4 -Einheiten im Verhältnis 1 : 1 besteht, die entlang BaB 2 S 4 : The first non-oxidic Chalcogenoborate with Boron in a trigonal-planar and tetrahedral CoordinationAbstract. Hitherto we know boron in a trigonal-planar and a tetrahedral coordination within one crystal structure from boron oxides in various compounds. With the novel bariummetathioborate BaB 2 S 4 we now report a crystal structure containing BS 3 and BS 4 units in the ratio 1 : 1 forming infinite chains along [001]. BaB 2 S 4 was synthesized in a solid state reaction at a temperature of 800°C from barium sulfide, amorphous boron and sulfur and crystallizes Einleitung

Structure Structure D 2000BaB 2 S 4 : The First Non-oxidic Chalcogenoborate with Boron in a Trigonal-Planar and Tetrahedral Coordination. -The title compound is prepared by solid state reaction of barium sulfide, amorphous boron, and sulfur (sealed quartz tube, 800°C, 2 h). BaB 2 S 4 crystallizes in the monoclinic space group Cc with Z = 4. The structure contains infinite anionic chains of condensed trigonal-planar BS 3 and tetrahedral BS 4 units in a 1:1 ratio. -(HAMMERSCHMIDT, A.; DOECH, M.; WULFF, M.; KREBS*, B.; Z.