Fibroblast growth factor 9 (FGF9)-mediated neurodegeneration: Implications for progressive multiple sclerosis?

Aims: Fibroblast growth factor (FGF) signalling is dysregulated in multiple sclerosis (MS) and other neurological and psychiatric conditions, but there is little or no consensus as to how individual FGF family members contribute to disease pathogenesis. Lesion development in MS is associated with increased expression of FGF1, FGF2 and FGF9, all of which modulate remyelination in a variety of experimental settings. However, FGF9 is also selectively upregulated in major depressive disorder (MDD), prompting us to speculate it may also have a direct effect on neuronal function and survival.

Parallel mapping of optical near-field interactions by molecular motor-driven quantum dots.

In the vicinity of metallic nanostructures, absorption and emission rates of optical emitters can be modulated by several orders of magnitude. Control of such near-field light-matter interaction is essential for applications in biosensing, light harvesting and quantum communication and requires precise mapping of optical near-field interactions, for which single-emitter probes are promising candidates. However, currently available techniques are limited in terms of throughput, resolution and/or non-invasiveness.

Changes in microtubule overlap length regulate kinesin-14-driven microtubule sliding.

Microtubule-crosslinking motor proteins, which slide antiparallel microtubules, are required for the remodeling of microtubule networks. Hitherto, all microtubule-crosslinking motors have been shown to slide microtubules at a constant velocity until no overlap remains between them, leading to the breakdown of the initial microtubule geometry. Here, we show in vitro that the sliding velocity of microtubules, driven by human kinesin-14 HSET, decreases when microtubules start to slide apart, resulting in the maintenance of finite-length microtubule overlaps.

The dynamics of the monomeric restriction endonuclease BcnI during its interaction with DNA.

Endonucleases that generate DNA double strand breaks often employ two independent subunits such that the active site from each subunit cuts either DNA strand. Restriction enzyme BcnI is a remarkable exception. It binds to the 5΄-CC/SGG-3΄ (where S = C or G, '/' designates the cleavage position) target as a monomer forming an asymmetric complex, where a single catalytic center approaches the scissile phosphodiester bond in one of DNA strands.

Transport efficiency of membrane-anchored kinesin-1 motors depends on motor density and diffusivity.

In eukaryotic cells, membranous vesicles and organelles are transported by ensembles of motor proteins. These motors, such as kinesin-1, have been well characterized in vitro as single molecules or as ensembles rigidly attached to nonbiological substrates. However, the collective transport by membrane-anchored motors, that is, motors attached to a fluid lipid bilayer, is poorly understood.

Toward Self-Assembled Plasmonic Devices: High-Yield Arrangement of Gold Nanoparticles on DNA Origami Templates.

Plasmonic structures allow the manipulation of light with materials that are smaller than the optical wavelength. Such structures can consist of plasmonically active metal nanoparticles and can be fabricated through scalable bottom-up self-assembly on DNA origami templates. To produce functional devices, the precise and high-yield arrangement of each of the nanoparticles on a structure is of vital importance as the absence of a single particle can destroy the functionality of the entire device.

Simultaneous Single-Molecule Force and Fluorescence Sampling of DNA Nanostructure Conformations Using Magnetic Tweezers.

We present a hybrid single-molecule technique combining magnetic tweezers and Förster resonance energy transfer (FRET) measurements. Through applying external forces to a paramagnetic sphere, we induce conformational changes in DNA nanostructures, which are detected in two output channels simultaneously. First, by tracking a magnetic bead with high spatial and temporal resolution, we observe overall DNA length changes along the force axis.

The helicase-like domains of type III restriction enzymes trigger long-range diffusion along DNA.

Helicases are ubiquitous adenosine triphosphatases (ATPases) with widespread roles in genome metabolism. Here, we report a previously undescribed functionality for ATPases with helicase-like domains; namely, that ATP hydrolysis can trigger ATP-independent long-range protein diffusion on DNA in one dimension (1D). Specifically, using single-molecule fluorescence microscopy we show that the Type III restriction enzyme EcoP15I uses its ATPase to switch into a distinct structural state that diffuses on DNA over long distances and long times.

Scanning evanescent fields using a pointlike light source and a nanomechanical DNA gear.

The characterization of three-dimensional inhomogeneous illumination fields is a challenge in modern microscopy. Here we use a four-arm DNA junction as a nanomechanical translation stage to move a single fluorescent quantum dot through an exponentially decaying evanescent field. Recording the emission of the quantum dot within the evanescent field as well as under homogeneous illumination allows one to directly obtain the intensity distribution of the excitation field without additional deconvolution.

DNA cleavage site selection by Type III restriction enzymes provides evidence for head-on protein collisions following 1D bidirectional motion.

DNA cleavage by the Type III Restriction-Modification enzymes requires communication in 1D between two distant indirectly-repeated recognitions sites, yet results in non-specific dsDNA cleavage close to only one of the two sites. To test a recently proposed ATP-triggered DNA sliding model, we addressed why one site is selected over another during cleavage. We examined the relative cleavage of a pair of identical sites on DNA substrates with different distances to a free or protein blocked end, and on a DNA substrate using different relative concentrations of protein.

X-ray and NMR crystallography in an enzyme active site: the indoline quinonoid intermediate in tryptophan synthase.

Chemical-level details such as protonation and hybridization state are critical for understanding enzyme mechanism and function. Even at high resolution, these details are difficult to determine by X-ray crystallography alone. The chemical shift in NMR spectroscopy, however, is an extremely sensitive probe of the chemical environment, making solid-state NMR spectroscopy and X-ray crystallography a powerful combination for defining chemically detailed three-dimensional structures.

Efficient preparation of internally modified single-molecule constructs using nicking enzymes.

Investigations of enzymes involved in DNA metabolism have strongly benefited from the establishment of single molecule techniques. These experiments frequently require elaborate DNA substrates, which carry chemical labels or nucleic acid tertiary structures. Preparing such constructs often represents a technical challenge: long modified DNA molecules are usually produced via multi-step processes, involving low efficiency intermolecular ligations of several fragments.

Type III restriction enzymes cleave DNA by long-range interaction between sites in both head-to-head and tail-to-tail inverted repeat.

Cleavage of viral DNA by the bacterial Type III Restriction-Modification enzymes requires the ATP-dependent long-range communication between a distant pair of DNA recognition sequences. The classical view is that Type III endonuclease activity is only activated by a pair of asymmetric sites in a specific head-to-head inverted repeat. Based on this assumption and due to the presence of helicase domains in Type III enzymes, various motor-driven DNA translocation models for communication have been suggested.