Contents of this Issue:
1. Science Highlight —
Discovering the Many Sides of Cells
(contacts: D.A. Hattendorf, dahatten@stanford.edu;
W.I. Weis, bill.weis@stanford.edu)
 |
| Model for how Sro7 may coordinate release of the SNARE Sec9 with arrival
of a secretory vesicle.
[larger view] |
Within a cell, pockets called vesicles deliver proteins to the various surface membranes, fusing with the membrane to deliver its cargo. The mechanism behind how vesicles discriminate between the membranes-fusing with some but not with others-has been mostly a mystery.
Using SSRL Beam Line 11-1, Hattendorf and colleagues solved the crystal structure of a yeast cell protein key to the process of polarization, called Sro7p, which is also found widely in other organisms. It is known that the Sro7p protein is involved in vesicle-membrane fusion. This protein consists of two barrel shaped structures and an additional, unexpected feature— a "tail" consisting of 60 amino acids that is bound to the bottom surface of one of the barrels. The researchers found that this tail is responsible for regulating how Sro7p interacts with other proteins that are important for vesicle fusion. It is this property that may give vesicles the ability to preferentially fuse with some membranes and not others, allowing them to deliver proteins to the correct locations on the cell surface to establish cellular polarity.
To learn more about this research, recently published in the journal
Nature, see the full scientific highlight at:
http://www-ssrl.slac.stanford.edu/research/highlights_archive/sro7-snare.html
2. Science Highlight —
Floppy Hairs and Sound Waves
(contact: G.C.L. Wong, gclwong@uiuc.edu)
Scientists exploring the physics of hearing have found an underlying molecular
cause for one form of deafness. The team, led by Gerard Wong, Professor of
Materials Science and Engineering, of Physics, and of Bioengineering at the
University of Illinois at Urbana-Champaign, report their findings in the
February 2007 issue of the journal Physical Review Letters.
Results indicate that yttrium impurities are mostly present as individual,
oxygen-coordinated atoms at the titania surface (i.e., as YO6
groups) and
about 15% of the surface oxygen sites are bound to Y. Together with the
observation of the structural modification and phase transformation retardation
in complementary wide-angle x-ray scattering experiments for the study, the
researchers found that the low concentrations of yttrium surface impurities on
nano-anatase reduce surface energy and inhibit nanoparticle growth over a large
temperature range. The findings demonstrate the effectiveness of surface bound
impurities of stabilizing nanoparticle size and phase, an issue of great
importance for retaining the materials properties of nanoscale catalysts that
operate at high temperatures.
To learn more about this research, recently published in the journal,
Physical Review Letters, see the full scientific highlight at:
"This is a first step," said physicist John Schmerge who worked on the project.
"Basically what we've done is turn off the heater and put in a laser."
The Linac Coherent Light Source (LCLS) injector gun already in operation also
uses a laser to produce electrons. In fact, the laser used by Schmerge and
colleagues is the same one used to test the LCLS prototype electron gun.
SPEAR3 is designed to operate at a current of 500 mA, but at the moment the
synchrotron is limited to 100 mA until the upgrade of a few systems to
accommodate the higher power is completed and required safety reviews have been
performed and approaches approved. Running at 500 mA, the present scheme of
refilling the ring three times a day would cause a large variation of beam
power on delicate x-ray optics between fills, reducing beam stability and data
quality. Upgrading the electron gun to operate by laser will enable SPEAR3's
operators to inject new current into the ring, not only much more quickly, but
more frequently and in shorter intervals to reduce the variation of stored
current between injection cycles—a process called "top off injection." This
rapid mode of injection will minimize the thermal strain on delicate optics and
will even out disruption to the users as the storage ring current is maintained
at a nearly constant level.
The 2007 Structural Molecular Biology (SMB) Summer School, co-chaired by Serena
DeBeer George, Clyde Smith, and Thomas Weiss, will be held September 9-14, 2007
at SSRL. The SMB Summer School will highlight the use and application of x-ray
absorption spectroscopy, macromolecular crystallography, and small angle x-ray
scattering. Presentations from experts in the fields will be aimed at the
graduate student level, but will also be appropriate for researchers with more
Awards for outstanding technical and scientific accomplishments in synchrotron
radiation-based science will be presented the evening of Tuesday, October 2,
immediately preceding the meeting dinner. Please take a few minutes to
recognize your colleagues' outstanding contributions by nominating them for the
following awards:
More information and registration for all of these events can be found at:
A two-day workshop on STXM and x-ray nanoprobe geo-, environmental, and
biological science was hosted by SSRL at the Bechtel International Center,
Stanford Campus, on July 9-10, 2007. The workshop brought together 49 leading
international STXM experts and scientists from three continents to explore
future possibilities, challenges and needs for STXM in these scientific areas.
The keynote talk was given by Harald Ade (NCSU). Subjects explored in detail
included scientific drivers, optics and beam design, end station
instrumentation and detectors. An extensive review of STXM and nanoprobe
facilities in Europe and North America was presented by members of the
respective facility teams. Key conclusions from the workshop include the
finding that there is overwhelming demand for beam time at high-resolution
spectromicroscopy facilities, that the present spatial resolution limit of 20
to 40 nm provides critical capabilities for a wide range of scientific
problems, but that 5 to 10 nm resolution (expected in the next few years) will
open exploration of new types of scientific problems, that the ability to
quickly measure K-edge spectra from C and elements up through S, Ca, and Fe
(~250 through 7200 eV) is of paramount importance, but that there is no
existing single facility that provides such capability.
The workshop was supported by DOE offices of Basic Energy Science and
Biological and Environmental Research.
A workshop report will be available at:
The SSRL Users' Organization Executive Committee (SSRLUOEC) met on Friday, July
20. Plans for the September 28-October 3 Special Symposium, SSRL/LCLS Users'
Meeting, and Workshops were discussed.
http://www-conf.slac.stanford.edu/ssrl-lcls/2007/
Other topics included undergraduate research and user suggestions from the user
survey which was conducted in January 2007 and completed by 370 users. Results
comprising users' opinions on scientific areas, proposed facilities and
initiatives, SSRL operations, and user resources were presented at the February
2007 meeting of the SSRL Scientific Advisory Committee (SAC). The presentation
itself can be found on the SSRLUOEC website at:
Hendrik Ohldag joined the meeting to summarize the July 9-10 Workshop on STXM
and X-ray Nanoprobe Capabilities and Needs for Geo-, Environmental, and
Biological Sciences. And, Apurva Mehta gave a presentation on the New
Directions in X-ray Scattering Workshop held last December.
Notes from SSRLUOEC meetings are posted on the web at:
The SSRLUOEC is currently seeking nominations to fill two SSRLUOEC positions
later this year (environmental sciences and macromolecular crystallography).
Ballots will be distributed in September, and candidates will be elected by the
SSRL user community by majority vote. Election results will be announced
during the annual Users' Meeting. The next SSRLUOEC meeting will be held on
the afternoon of Tuesday, October 2.
SSRL's current experimental run ends at 6:00 am on Monday, August 6; user
operations will resume on most beam lines in early November 2007. The FY2008
SPEAR3 preliminary operating schedule which includes information on scheduled
maintenance and accelerator physics studies is available at:
http://www-ssrl.slac.stanford.edu/schedules/07-08_run.pdf
Spokespersons with active proposals who are interested in requesting beam time
on X-ray/VUV beam lines for the next scheduling period (November 2007-January
2008) must submit beam time request by the August 17 deadline.
A message will be sent to Macromolecular Crystallography spokespersons in
August regarding Beam Time Requests for the first scheduling period in the
FY2008 experimental run.
__________________________________________________________________________
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the DOE
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Filamentous actin (F-actin) is a rod-like protein that provides structural
framework in living cells. F-actin is organized into bundles by actin binding
proteins, such as espin, a linker protein found in sensory cells, including
hair cells in the cochlea of the inner ear. Within the cochlea, sound waves
stimulate the hair cells and trigger nerve impulses that are transmitted to the
brain.
(a) Diffraction from partially
oriented F-actin-espin bundles shows many hexagonally coordinated peaks. The
reconstructed 3D bundle structure is approximated in (b). (c) Diffraction from
F-actin complexed with mutant espin. The diffraction pattern only shows a
"bow-tie" pattern which is indicative of a liquid crystalline nematic phase,
like that shown in (d). The mutant espins only weakly crosslink the actin
filaments, but the normal espins arrange the actin into tight crystalline
bundles.
Using small-angle x-ray scattering experiments at SSRL's Beam Line 4-2 and at
APS, Wong's team solved the structure of various espin-actin bundles. The team
learned that mutations in espin can cause actin in the bundles to 'melt' into a
liquid crystal (the kind of molecular organization in a liquid crystal laptop
screen), thereby making these bundles of protein filaments within the cochlear
hair cells much floppier, impairing the passage of vibrations and resulting in
deafness.
To learn more about this research see the full scientific highlight at:
http://www-ssrl.slac.stanford.edu/research/highlights_archive/actin-espin.html
3. Science Highlight —
A Surprising Behavior of Yttrium Impurities
(contacts: B. Chen, binchen@eps.berkeley.edu;
J. Banfield, jill@eps.berkeley.edu)
Structurally incorporated impurities have been shown to have systematic effects
on the rate of the thermally driven transformations in titania nanoparticles.
For example, the anatase-to-rutile transformation is slowed when anatase
nanoparticles are doped with a cation of valence > +4, but favored when the
valence < +4. Based on these observations, Y3+ dopants should
promote the anatase-to-rutile transformation. However, prior studies showed
that the transformation is actually inhibited by such impurities. So far these
observations have remained unexplained.
The EXAFS experimental setup.
Recently, scientists from University of California Berkeley and Lawrence
Berkeley National Laboratory, in collaboration with SSRL beam line scientists
at BLs 10-2 and 11-2, used extended x-ray absorption fine structure (EXAFS)
experiments on yttrium-doped titania nanoparticles to determine the local
structural environment of Y3+ impurities.
http://www-ssrl.slac.stanford.edu/research/highlights_archive/ydopants.html
—Brad Plummer, SLAC Today, July 12, 2007
Last month a small team of SLAC physicists conquered another challenge in the
quest to take the SPEAR3 synchrotron permanently up to its full operational
capability of 500 milliamperes (mA). Using the existing electron gun and
accelerator, the team demonstrated that a laser can be used to create a large
pulse of electrons, which will aid rapid injection of beam into the ring.
John Schmerge in the SPEAR3 injector vault with the laser setup and cathode gun
used to test a new method of generating electrons.
As it now operates, SPEAR3's electron gun produces electron pulses as the gun's
cathode is heated to nearly 2,000 degrees Fahrenheit (1,050 Celsius). This
configuration allows only minimal control over the timing and the amount of
power in each pulse because the hot cathode continually emits a pulsed stream
of a few thousand electron bunches, of which only five or six are useable for
injection into the SPEAR3 storage ring. Using a brief laser pulse to stimulate
a burst of electrons eliminates limitations associated with a hot cathode,
producing a single, precise electron microbunch with much higher charge.
5.
Pottery Shards Reveal Clues about the Rise and Fall of the Roman Empire
—Brad Plummer, SLAC Today, July 25, 2007
Call it old-school outsourcing - more than 2,000 years ago, the Roman Empire
exploited the labor of artisans in southern Gaul (modern-day France) to
mass-produce a particular style of Italian pottery craved by the Roman
populace. Now, synchrotron light is helping to detail the particulars of how
this pottery was produced and how the method of production and quality of the
ware reflects the rise and fall of the Roman Empire.
Phillipe Goudeau (left) and Phillipe Sciau visited SSRL in early July to study
fragments of ancient pottery. Here, Sciau holds a replica of the clay pots.
"This pottery and how it is made—how the technology developed and
declined—gives us clues about the end of the Roman Empire," says Philippe
Sciau, one of two visiting researchers from the National Center for Scientific
Research (CNRS) in France.
The design of the pottery originated in Northern Italy, but as demand rose,
factory ovens for mass production were built in southern Gaul. The Romans
conscripted Gaulish workers to fire as many as 30,000 pieces at a time in these
enormous ovens. Read more at:
http://today.slac.stanford.edu/feature/2007/ssrl-pottery.asp
6.
Apply Now for SSRL Structural Molecular Biology Summer School
(contact: S. DeBeer George, serena@slac.stanford.edu)
extensive experience in one of these techniques with an interest in
using other complementary methods to further the scope of their research.
For more information and to apply, see:
http://www-conf.slac.stanford.edu/smb-ss/2007
The six-day school will consist of three days of lectures from experts in the
field, followed by three days of hands-on practical sessions. Enrollment will
be limited, so prospective participants should apply by the August 15, 2007
deadline.
7.
Register for 2007 SSRL/LCLS Users' Meeting and Workshops
(contact:
C. Knotts, knotts@slac.stanford.edu)
There are several very exciting events planned for the upcoming SSRL/LCLS
Users' Meeting, beginning with a special symposium on September 28-29 to look
into the future of x-ray science.
A joint SSRL/ALS Workshop on Synchrotron Techniques will follow on Sunday,
September 30. The workshop will provide a tutorial-style basic introduction to
the various experimental techniques available at synchrotron facilities, with
the goal of helping users make the most out of their beam time.
The main Users' Meeting, on October 1-2, will feature presentations on recent
developments and new opportunities in structural biology and spectroscopy,
material and environmental science, ultrafast science and LCLS instrumentation.
A special keynote presentation will be given by Nobel Laureate Professor Roger
Kornberg. Share your recent research results at the Users' Meeting by
submitting an abstract for oral or poster presentation, due August 15 and
September 4, respectively. Don't forget that the 2007 SSRL/LCLS dinner is free
for students who submit an abstract! (send abstracts to
lisa@slac.stanford.edu)
Several concurrent workshops will be offered on October 3: XANES Spectroscopy
(Data Collection, Analysis, and Simulation); Microfocusing; Imaging and X-ray
Microscopy; and Research Opportunities at the X-ray Pump-Probe Facility at the
LCLS.
http://www-conf.slac.stanford.edu/ssrl-lcls/2007/
8.
Workshop on STXM and X-ray Nanoprobe Capabilities and Needs for Geo-,
Environmental, and Biological Sciences Held in July
(organizers:
S. DeBeer George, serena@slac.stanford.edu;
J. Bargar, bargar@slac.stanford.edu;
H. Ohldag, hohldag@slac.stanford.edu)
http://www-ssrl.slac.stanford.edu/conferences/workshops/stxm2007/index.php
9.
SSRL Users' Organization Update
(contacts:
C.S. Kim (SSRLUOEC Chair), cskim@chapman.edu;
C. Knotts, knotts@slac.stanford.edu)
http://www-ssrl.slac.stanford.edu/users/ssrluo/
http://www-ssrl.slac.stanford.edu/conferences/workshops/stxm2007/index.php
http://www-ssrl.slac.stanford.edu/conferences/workshops/newdirections2006/index.php
http://www-ssrl.slac.stanford.edu/users/ssrluo/ssrluo-minutes.html
http://www-conf.slac.stanford.edu/ssrl-lcls/2007/nomination.htm
10.
User Administration Update
(contacts:
C. Knotts, knotts@slac.stanford.edu; L. Dunn, lisa@slac.stanford.edu)
http://www-ssrl.slac.stanford.edu/users/user_admin/xray_btrf.html
http://www-ssrl.slac.stanford.edu/users/user_admin/vuv_btrf.html
11.
Photon Science Job Opportunities
A number of positions are currently available at SSRL and LUSI.
Please refer to the Photon Science Job Openings page for more information about
these job opportunities.
http://photonscience.slac.stanford.edu/jobs.php
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