Download Abstracts - Weizmann Institute of Science

Didi Margulies
Dept. of Organic Chemistry
Using Synthetic Molecules to Communicate with Proteins and
Make Them Talk to Each Other
Our group's research is concerned with diverse aspects of bioorganic chemistry, with
emphasis on designing synthetic receptors that interact with proteins and sense or
regulate their function. In this talk I will give a brief overview of the novel classes of
fluorescent molecular sensors that we developed over the last few years, and show
how they can be used to detect individual proteins, protein combinations, as well as
dynamic changes that occur on their surfaces. In the second part of this talk I will
describe the first step toward establishing artificial signal transduction pathways.
Specifically, I will discuss the design and operating principles of a synthetic ‘chemical
transducer’ that can generate (in vitro) an artificial communication channel between
two unrelated proteins.
Hagen Hofmann
Dept. of Structural Biology
Single-molecule dynamics in transcription factor interactions
Genomic and proteomic methods have afforded a wealth of genetic network
architectures in systems biology. However, the mechanisms of how genes are
actually switched on and off are much less understood. At a molecular level, this
understanding is particularly complicated by the multi-functionality of many
transcription factors, which is typically mediated by disordered regions with
substantial flexibility. In the first part of the talk, I demonstrate that single-molecule
fluorescence methods are ideal to quantify this flexibility. Using single-molecule
Förster resonance energy transfer (FRET), fast large-scale distance dynamics on a
sub-microsecond timescale are identified in the high-affinity complex of the
interaction domains of CBP/p300 and ACTR, a p160 coactivator. Mapping three
distances at the same time in a three-color FRET approach additionally shows that
the observed motions are collective, suggesting that high-affinity and high flexibility
are not mutually exclusive. In the second part of my talk, I present future targets of
our single-molecule approach that aims to link the dynamics of gene activation to the
biological phenotype of simple organisms.
Yohai Kaspi
Dept. of Earth and Planetary Sciences
Jets and macroturbulence in the atmosphere
Atmospheric jets carry the bulk of momentum, heat and moisture in the extratropics,
and are therefore dominant in the dynamics of midlatitude climate. Jets are also
prominent in other planetary atmospheres in the Solar System such as those of
Jupiter and Saturn, and have been shown to exist on exoplanets as well. In this talk, I
will discuss mechanisms for formation of atmospheric jets, and show recent work
where we explained the poleward migration of zonal wind anomalies in the
atmosphere as poleward migration of eddy-driven jets. We provide a mechanism for
the migration using idealized General Circulation Model simulations at high rotation
rates, where the fast rotation allows to separate the eddy-driven and subtropical jets.
Using multiple-jet simulations we show how inverse cascades and macroturbulence
control the meridional scale of the jets, and how energy is partitioned and transferred
up and down scale through eddy-eddy and eddy-mean interactions at different
latitudinal regimes.
Oren Tal
Dept. of Chemical Physics
New electronic transport effects in atomic and molecular
conductors
The study of electronic transport at the scale of atoms and molecules allows the
demonstration of new material properties, fundamental quantum effects, and general
strategies for controlling electronics at the ultimate limit of miniaturization. I will
review several recently discovered effects, including the onset of conductance
saturation across pi-conjugated molecules, electron-vibration interaction in a
molecular-based many-body electronic system, remarkable enhancement of
magnetoresistance by molecules and the emergence of half-metallicity (i.e., perfect
spin filtering) in atomic scale nickel-oxide. This diverse range of phenomena is
achieved by different manifestations of selective orbital hybridization, paving the way
for controlled atomic scale electronic transport by “orbital engineering”.
Barak Dayan
Dept. of Chemical Physics
Controlling Light with Light: Demonstration of Deterministic
Photon-Photon Interactions
Controlling light with light at the level of single photons, namely obtaining
deterministic photon-photon interactions, has been the goal of extensive research
efforts worldwide in the last couple of decades. I will present our recent
demonstration of deterministic photon-photon interactions based on a single atom.
We use ultrahigh quality chip-based optical microresonator to couple light from an
optical nano-fiber to a single atom. our device then operates as a single-photon
toggle-switch: the first photon arriving from one direction of the fiber is reflected by
the atom, and any subsequent photons are transmitted. To toggle the state back a
photon is simply sent to the atom from the other direction of the fiber – truly control of
one (or more) photons just by the command of another single photon. Based on a
novel mechanism of passive, interference-based nonlinearity, this scheme requires
no control fields, and can function as a quantum memory and even a universal
quantum gate. It can therefore provide a building block for scalable quantum
networks based on completely passive photonic devices interconnected and
activated solely by single photons
Refs:
[1] S. Rosenblum, A. S. Parkins, and B.Dayan, "Photon routing in cavity QED: Beyond the
fundamental limit of photon blockade", Phys. Rev. A. 84, 033854 (2011)
[2] I. Shomroni, S. Rosenblum, Y. Lovsky, O. Bechler, G. Guendelman, and B. Dayan,
"All-optical routing of single photons by a one-atom switch controlled by a single photon",
Science 345, 903 (2014)
Emmanuel Levy
Dept. of Structural Biology
Functional, dysfunctional
assemblies.
and
engineered
protein
super-
A single yeast cell is a few microns in diameter and yet contains about a hundred million
proteins. Interactions between these proteins are crucial for most cellular functions,
which has fuelled efforts to characterize how proteins assemble into functional
complexes. Considerable information thus exists on the composition and structure of
protein complexes, but less is known about their higher-order organization in living cells
– i.e., we know much about “teams” of proteins, but we know little about how they
collaborate with other teams.
We will present work that aims to better understand this high-order organization. First,
we will describe a strategy to probe the local environment of proteins in living cells, and
thereby measure functional interactions. Second, we will discuss the narrow gap that
separates functional and dysfunctional interactions, by showing that single point
mutations frequently lead to uncontrolled protein super-assembly. Finally, we will present
a synthetic system consisting of two proteins engineered to self-assemble into micronscale compartments. Taken together, these studies contribute to our understanding of
how the cellular machinery is organized, and what challenges and opportunities it faces
during its evolution.
Rafal Klajn
Dept. of Organic Chemistry
Dynamically self-assembling nanoflasks
Chemists seek to mimic the approach of natural systems, which utilize the effects of
nanoscale confinement to perform chemical reactions at astonishing rates and
selectivities and to synthesise complex molecules. To this end, chemists have
synthesized a variety of nanostructured materials, such as colloidal crystals selfassembled from inorganic nanoparticles, that typically feature nanosized pores in
which chemical reactions could potentially be accelerated. However, product
inhibition and the slow diffusion rate into and out of the pores hamper progress. We
have shown that colloidal crystal “nanoflasks” created by UV illumination of
appropriate nanoparticles occlude small molecules from the surrounding solution
such that they undergo chemical reactions with greatly increased kinetics and
different stereoselectivities from those in solution. Illumination with visible light
disassembles the nanoflasks, releases the product into solution and thereby
establishes a catalytic cycle. This novel method avoids problems associated with
product inhibition and overcomes the diffusion limitation. Furthermore, the
dynamically self-assembling nanoflasks have tuneable dimensions and offer a
powerful tool for studying chemical reactivities in confined environments and for
synthesising diverse classes of molecules.
Assaf Tal
Dept. of Chemical Physics
Nuclear Magnetic Resonance as a Tool for Probing In-vivo
Brain Metabolism
Magnetic resonance can be used in-vivo to probe the brain's biochemistry and metabolism.
This is achieved by shaping the electromagnetic fields inside an MRI scanner in order to
coherently control the nuclear spins' time dynamics. This talk will outline some of our work on
fast, high-quality pulse sequences specifically tuned for imaging real time metabolic changes
and hard-to-detect metabolites, and sketch some of the future applications of these
methodologies.
Ron Diskin
Dept. of Structural Biology
Structural insights for Old World Arenaviruses
A crucial step in the life cycle of a virus is its ability to recognize and attach to its host
cell. Viral glycoproteins that we study in our lab play a major role in this process.
They are located on the viral membrane and specifically recognize their host cell
receptors by forming specific molecular complexes. We aim to understand the
molecular mechanisms underlying viral tropism and pathogenicity. In my talk I will
describe some of our recent progress in understanding the molecular mechanisms
for Lassa virus infection. I will also describe a few of our current ongoing efforts to
characterize Arenavirus-derived glycoproteins.
Amnon Bar-Shir
Dept. of Organic Chemistry
“Multicolor” Imaging Sensors: Beyond “Monochromatic” MRI
Genetically engineered optical reporters (i.e., reporter genes) have become the felt
highlighter pens of science, since they enable to tag molecules (or cell) of interest
with striking contrast to show their location, levels and roles in colorful relief. The
evolution of the green fluorescent protein (GFP) as reporter gene and the extension
of the fluorescent proteins palette beyond green allow scientists to give multiple
proteins and cells variable colors and follow several different biological processes
simultaneously. Nevertheless, their light signal source restricts their ability to
penetrate tissues and excludes detectability from deep biological organs.
Developing novel genetically engineered reporter systems for MRI can dramatically
improve our ability to follow dynamic gene expression changes non-invasively, in
deep tissues, and combine sub-cellular information with high spatial resolution
anatomical images. After decades of using gadolinium- or iron-based metallic
sensors for MRI, the recently developed chemical exchange saturation transfer
(CEST) contrast mechanism has created an opportunity for rational design of nonmetallic biosensors for MRI.
The CEST approach allows the use of bioorganic molecules as the contrast
enhancers that generate a frequency-encoded contrast in MRI, which tolerates their
simultaneous monitoring. Since CEST-MRI sensors are chemically tunable and
biochemically compatible, they enable spatially mapping of reporter genes
expression with a novel and fundamental “multicolor” feature.
Itay Halevy
Dept. of Earth and Planetary Sciences
Microbial to global insights into the sulfur cycle
The sulfur cycle shuttles large masses of material through Earth's surface
environment, influencing the chemical composition of seawater, the oxidation state of
the oceans and atmosphere and the biogeochemical cycles of other major redoxsensitive elements, such as carbon and iron. Information about the long-term
operation of these large-scale processes is encoded in the geologic record of sulfur
isotopes, which can only be read given an understanding of the major sources and
sinks of sulfur and of the processes that fractionate sulfur isotopes. These processes
operate over a wide range of spatio-temporal scales, from the microbial, to the global
ocean and sedimentary rock reservoir. Novel theoretical understanding of sulfur
isotope fractionation during microbial sulfate reduction, coupled with data from ocean
sediment cores and reactive transport models of the sediment column, suggests a
muted record of large inherent microbial fractionations. The much smaller and more
variable apparent fractionation of sulfur isotopes observed in present-day natural
environments and preserved in the geologic record, does not, as previously
suggested, directly reflect variability in environmental sulfate concentrations or in the
rates of microbial sulfate respiration. Instead, these records reflect the degree of
exchange of sulfate and sulfide between seawater and sediment porewater and may
allow reconstruction of seawater sulfate concentrations over Earth history.