Halogenated natural products play important roles as antibiotics, antifungals, and antitumor agents. The process of halogenation involves the replacement of a hydrogen with a halide (such as chloride or bromide), and is a challenging task for a synthetic chemist. However, the iron-containing enzymes in the haloperoxidase and halogenase families readily catalyze these reactions. It is thought that when this reaction occurs, the iron in the enzyme is at a high-valent Fe(IV) state, and that this species is responsible for removing a hydrogen atom (called an abstraction) from the substrate, creating a substrate radical, and that a halogen radical is subsequently transferred to the substrate to complete the halogenation reaction.
Approximately 1,600 scientists visit SSRL annually to conduct experiments in broad disciplines including life sciences, materials, environmental science, and accelerator physics. Science highlights featured here and in our monthly newsletter, Headlines, increase the visibility of user science as well as the important contribution of SSRL in facilitating basic and applied scientific research. Many of these scientific highlights have been included in reports to funding agencies and have been picked up by other media. Users are strongly encouraged to contact us when exciting results are about to be published. We can work with users and the SLAC Office of Communication to develop the story and to communicate user research findings to a much broader audience. Visit SSRL Publications for a list of the hundreds of SSRL-related scientific papers published annually and to add your most recent publications to this collection.
While we continue to refine our science highlights content you may access older science summaries that date between 04/2001 to 06/2010 by visiting http://www-ssrl.slac.stanford.edu/science/sciencehighlights.html. We will be offering science summaries that date from 06/2012 to the present soon.
March 2008
X-ray Absorption Spectroscopy
BL7-3
March 2008
New approaches to the fabrication of ferroelectric nanostructures onto substrates are critical for the development of competitive functional devices that successfully integrate at nanoscale ferroelectrics as alternative materials in the microelectronic industry. These approaches have to meet reliability and utilization requirements to realize a cost-effective production of an increasing demand for ultra-high-density memories or nanometric electromechanical systems. An important challenge in the fabrication of ferroelectric nanomaterials supported onto substrates is the ability to fabricate an organized arrangement of the nanostructures. This is a key point for the applications of ferroelectrics in nanoelectronic devices.
BL11-3
February 2008
A collaboration between scientists at SSRL and the department of Applied Physics at Stanford University has determined the phase diagram of a new family of prototypical charge density wave (CDW) compounds. These compounds have the chemical formula RTe3, where R represents a rare earth element from La to Tm. In research, the collaborators have used X-ray diffraction and resistivity measurements to determine the factors affecting the symmetry of the CDW state, specifically whether the CDW runs in one direction or two.
X-ray diffraction
BL7-2, BL11-3
February 2008
The development of bacterial resistance to conventional antibiotics is a major public health concern. For example, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE) and Staphylococcus aureus (VRSA) have emerged as common nosocomial (hospital-originating) infections. Circumvention of such resistance may be possi ble by emulating host defense antimicrobial peptides (AMP's), which are found in a broad range of species and have broad-spectrum antimicrobial properties. These AMP's have two structural motifs in common: they are cationic and amphipathic. It is thought that electro static interactions facilitate association of the peptide with the anionic bacterial membrane and amphiphilic interactions act to form pores in the bacterial membrane, leading to cell death.
Biological Small-angle X-ray Scattering (BioSAXS)
BL4-2
January 2008
Proteins are transported to specific sites within cells enclosed in packets called transport vesicles, along a specialized network of tracks called microtubules. Transport vesicles are targeted to the correct acceptor membrane by a number of sequential steps that are regulated by small GTPases of the Rab and Arf families. The initial interaction between vesicles and the target membrane is thought to be mediated by very large molecular "tethers" that link the two membranes prior to fusion. A Stanford team from the Brunger and Pfeffer laboratories has studied how one such putative tether molecule is localized to the membranes of an organelle called the Golgi complex.
Macromolecular Crystallography
BL7-1, BL11-1
January 2008
Life depends on the biochemical activity of the thousands of proteins that inhabit and decorate the surface of every one of our cells. Proteins themselves, although simple linear combinations of the twenty amino acids, derive their remarkable properties from the complex three-dimensional structures into which they fold. In this way, enzyme active sites are created, protein-protein recognition surfaces are formed, and the chemistry of life is set in motion.
Macromolecular Crystallography
BL11-1
December 2007
Autism is a neurodevelopmental disorder that impairs social interactions, and causes communication deficits and repetitive behaviors. About 1 in every 150 children is affected by autism. Genetic screens revealed that mutations in the neurexin and neuroligin genes are among the multiple genetic causes of autism spectrum disorders and mental retardation (Jamain et al., 2003; Szatmari et al., 2007). In the brain, neurexins and neuroligins are cell adhesion proteins on the pre-synaptic and post-synaptic cell membranes, respectively. Their extracellular domains interact with each other within the synaptic cleft to provide connectivity between nerve cells and assure proper synapse function.
Macromolecular Crystallography
BL11-1
December 2007
A team of scientists, working in part at SSRL's crystallography beam lines and led by Stanford Professor Roger Kornberg, has determined for the first time the atomic structure (at 1.1 Å resolution) of a thiol-covered gold nanoparticle, a discovery with potential for a range of applications from biosensors to nanotransistors. The results are published in the October 19 issue of Science.
Macromolecular Crystallography
BL11-1, BL11-3
November 2007
Since the discovery of high-temperature superconductor by Bednorz and Müller in 1986, this field has become one of the most important research topics in solid state physics. In the past 20 years many unconventional properties have been discovered in this new class of materials. These have challenged our conventional wisdom and driven the development of many novel theories. Among these discoveries, the most mysterious is probably the pseudogap phenomena: it has been observed that there is an energy gap above the superconducting transition temperature (TC) that persists over a wide range of temperatures and chemical compositions [1]. This peculiar behavior appears to be very different from a conventional superconductor. Here the electrons form so-called "Cooper pairs", which manifests itself as an energy gap in many spectroscopic measurements.
Angle-resolved photoelectron spectroscopy
BL5-4
November 2007
Proteins containing iron-sulfur clusters are ubiquitous in nature and catalyze one-electron transfer processes. These proteins have evolved into two classes that have large differences in their electrochemical potentials: high potential iron-sulfur proteins (HiPIPs) and bacterial ferredoxins (Fds). The role of the surrounding protein environment in tuning these redox potentials has been a persistent puzzle in the understanding of biological electron transfer. Although high potential iron-sulfur proteins and ferredoxins have the same iron-sulfur structural motif, there are large differences in their electrochemical potentials.
X-ray Absorption Spectroscopy
BL6-2
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