Bdellovibrio predation cycle characterized at nanometre-scale resolution with cryo-electron tomography.

Bdellovibrio bacteriovorus is a microbial predator that offers promise as a living antibiotic for its ability to kill Gram-negative bacteria, including human pathogens. Even after six decades of study, fundamental details of its predation cycle remain mysterious. Here we used cryo-electron tomography to comprehensively image the lifecycle of B.

X-Ray Crystallographic Analysis of NifB with a Full Complement of Clusters: Structural Insights into the Radical SAM-Dependent Carbide Insertion During Nitrogenase Cofactor Assembly.

NifB is an essential radical SAM enzyme required for the assembly of an 8Fe core of the nitrogenase cofactor. Herein, we report the X-ray crystal structures of Methanobacterium thermoautotrophicum NifB without (apo MtNifB) and with (holo MtNifB) a full complement of three [Fe S ] clusters. Both apo and holo MtNifB contain a partial TIM barrel core, but unlike apo MtNifB, holo MtNifB is fully assembled and competent in cofactor biosynthesis.

Identity and function of an essential nitrogen ligand of the nitrogenase cofactor biosynthesis protein NifB.

NifB is a radical S-adenosyl-L-methionine (SAM) enzyme that is essential for nitrogenase cofactor assembly. Previously, a nitrogen ligand was shown to be involved in coupling a pair of [FeS] clusters (designated K1 and K2) concomitant with carbide insertion into an [FeSC] cofactor core (designated L) on NifB. However, the identity and function of this ligand remain elusive.

Structural and Mechanistic Insights into CO Activation by Nitrogenase Iron Protein.

The Fe protein of nitrogenase catalyzes the ambient reduction of CO when its cluster is present in the all-ferrous, [Fe S ] oxidation state. Here, we report a combined structural and theoretical study that probes the unique reactivity of the all-ferrous Fe protein toward CO . Structural comparisons of the Azotobacter vinelandii Fe protein in the [Fe S ] and [Fe S ] states point to a possible asymmetric functionality of a highly conserved Arg pair in CO binding and reduction.

Structural Analysis of a Nitrogenase Iron Protein from Methanosarcina acetivorans: Implications for CO Capture by a Surface-Exposed [FeS] Cluster.

Nitrogenase iron (Fe) proteins reduce CO to CO and/or hydrocarbons under ambient conditions. Here, we report a 2.4-Å crystal structure of the Fe protein from (NifH), which is generated in the presence of a reductant, dithionite, and an alternative CO source, bicarbonate.

Strategies Towards Capturing Nitrogenase Substrates and Intermediates via Controlled Alteration of Electron Fluxes.

Nitrogenase utilizes an ATP-dependent reductase to deliver electrons to its catalytic component to enable two important reactions: the reduction of N to NH , and the reduction of CO to hydrocarbons. The two nitrogenase-based reactions parallel the industrial Haber-Bosch and Fischer-Tropsch processes, yet they occur under ambient conditions. As such, understanding the enzymatic mechanism of nitrogenase is crucial for the future development of biomimetic strategies for energy-efficient production of valuable chemical commodities.

Probing the coordination and function of FeS modules in nitrogenase assembly protein NifB.

NifB is an essential radical S-adenosylmethionine (SAM) enzyme for nitrogenase cofactor assembly. Previous studies show that NifB couples a putative pair of [FeS] modules (designated K1 and K2) into an [FeSC] cofactor precursor concomitant with radical SAM-dependent carbide insertion through the action of its SAM-binding [FeS] module. However, the coordination and function of the NifB cluster modules remain unknown.

In Vivo Structures of the Helicobacter pylori cag Type IV Secretion System.

The type IV secretion system (T4SS) is a versatile nanomachine that translocates diverse effector molecules between microbes and into eukaryotic cells. Here, using electron cryotomography, we reveal the molecular architecture of the Helicobacter pylori cag T4SS. Although most components are unique to H.

Cluster assembly in nitrogenase.

The versatile enzyme system nitrogenase accomplishes the challenging reduction of Nand other substrates through the use of two main metalloclusters. For molybdenum nitrogenase, the catalytic component NifDK contains the [FeS]-core P-cluster and a [MoFeSC-homocitrate] cofactor called the M-cluster. These chemically unprecedented metalloclusters play a critical role in the reduction of N, and both originate from [FeS] clusters produced by the actions of NifS and NifU.

structures of an intact type VI secretion system revealed by electron cryotomography.

The type VI secretion system (T6SS) is a versatile molecular weapon used by many bacteria against eukaryotic hosts or prokaryotic competitors. It consists of a cytoplasmic bacteriophage tail-like structure anchored in the bacterial cell envelope via a cytoplasmic baseplate and a periplasmic membrane complex. Rapid contraction of the sheath in the bacteriophage tail-like structure propels an inner tube/spike complex through the target cell envelope to deliver effectors.

Architecture of the Vibrio cholerae toxin-coregulated pilus machine revealed by electron cryotomography.

Type IV pili (T4P) are filamentous appendages found on many Bacteria and Archaea. They are helical fibres of pilin proteins assembled by a multi-component macromolecular machine we call the basal body. Based on pilin features, T4P are classified into type IVa pili (T4aP) and type IVb pili (T4bP).

Architecture of the type IVa pilus machine.

Type IVa pili are filamentous cell surface structures observed in many bacteria. They pull cells forward by extending, adhering to surfaces, and then retracting. We used cryo-electron tomography of intact Myxococcus xanthus cells to visualize type IVa pili and the protein machine that assembles and retracts them (the type IVa pilus machine, or T4PM) in situ, in both the piliated and nonpiliated states, at a resolution of 3 to 4 nanometers.