No abstract

The carbon monoxide complex of [NiFe]hydrogenase from Desulfovibrio vulgaris Miyazaki F has been characterized by X-ray crystallography and absorption and resonance Raman spectroscopy. Nine crystal structures of the [NiFe]hydrogenase in the CO-bound and CO-liberated forms were determined at 1.2-1.4 A resolution. The exogenously added CO was assigned to be bound to the Ni atom at the Ni-Fe active site. The CO was not replaced with H(2) in the dark at 100 K, but was liberated by illumination with a strong white light. The Ni-C distances and Ni-C-O angles were about 1.77 A and 160 degrees, respectively, except for one case (1.72 A and 135 degrees ), in which an additional electron density peak between the CO and Sgamma(Cys546) was recognized. Distinct changes were observed in the electron density distribution of the Ni and Sgamma(Cys546) atoms between the CO-bound and CO-liberated structures for all the crystals tested. The novel structural features found near the Ni and Sgamma(Cys546) atoms suggest that these two atoms at the Ni-Fe active site play a role during the initial H(2)-binding process. Anaerobic addition of CO to dithionite-reduced [NiFe]hydrogenase led to a new absorption band at about 470 nm ( approximately 3000 M(-1)cm(-1)). Resonance Raman spectra (excitation at 476.5 nm) of the CO complex revealed CO-isotope-sensitive bands at 375/393 and 430 cm(-1) (368 and 413 cm(-1) for (13)C(18)O). The frequencies and relative intensities of the CO-related Raman bands indicated that the exogenous CO is bound to the Ni atom with a bent Ni-C-O structure in solution, in agreement with the refined structure determined by X-ray crystallography.

Bottom-up construction of giant structures by the self-assembly of a large number of components (n = 100) has been a daunting challenge. Here, Fujita and colleagues report the self-assembly of a spherical metal polyhedron, possessing a hitherto unreported icosidodecahedron geometry with 30 vertices and 60 edges. The authors succeeded in controlling the self-assembly by intensive tuning of the ligand flexibility. X-ray crystallographic analysis confirmed that the complex is the largest well-defined spherical molecular capsule, comparable with the size of a typical protein.

Protein encapsulation has long attracted many chemists and biologists because of its potential to control the structure and functions of proteins, but has been a daunting challenge because of their incommensurably larger size compared with common synthetic hosts. Here we report the encapsulation of a small protein, ubiquitin, within giant coordination cages. The protein was attached to one bidentate ligand and, upon addition of Pd(II) ions (M) and additional ligands (L), M(12)L(24) coordination nanocages self-assembled around the protein. Because of the well-defined host framework, the protein-encapsulated structure could be analysed by NMR spectroscopy, ultracentrifugation and X-ray crystallography.