How the membrane
protein AmtB
transports ammonia
Membrane proteins provide molecular-sized
entry and exit portals for the various substances that pass
into and out of cells. While life scientists have solved the
structures of protein channels for ions, uncharged solutes,
and even water, up to now they have only been able to guess
at the precise mechanisms by which gases (such as NH3,
CO2, O2, NO, N2O, etc.) cross
biological membranes. But, with the first high-resolution
structure of a bacterial ammonia transporter (AmtB), determined
by a team in the Stroud group from the University of California,
San Francisco, it is now known that this family of transporters
conducts ammonia by stripping off the proton from the ammonium
(NH4+) cation and conducting the uncharged
NH3 "gas." Full
story.
Publication about this research: S. Khademi,
J. O'Connell III, J. Remis, Y. Robles-Colmenares, L.J. Miercke,
and R.M. Stroud, "Mechanism of ammonia transport by Amt/MEP/Rh:
Structure of AmtB at 1.35 Å," Science 305,
1587 (2004).
Contact: Robert Stroud, stroud@msg.ucsf.edu
Energetics of
hydrogen bond network
rearrangements in liquid water
The unique chemical and physical properties
of liquid water are thought to result from the highly directional
hydrogen bonding (H-bonding) network structure and its associated
dynamics. However, despite intense experimental and theoretical
scrutiny, a complete description of this structure has been
elusive. Recently, with the help of their novel liquid microjet
apparatus, a University of California, Berkeley, group derived
a new energy criterion for H-bonds based on experimental data.
With this new criterion based on analysis of the temperature
dependence of the x-ray absorption spectra of normal and supercooled
liquid water, they concluded that the traditional structural
model of water is valid. Full
story.
Publication about this research: J.D.
Smith, C.D. Cappa, K.R. Wilson, B.M. Messer, R.C. Cohen, and
R.J. Saykally, "Energetics of hydrogen bond network rearrangements
in liquid water," Science 306,
851 (2004).
Contact: Richard Saykally, saykally@calmail.berkeley.edu
Substrate recognition
strategy
for botulinum neurotoxin
Clostridal neurotoxins (CNTs) are the
causative agents of the neuroparalytic diseases botulism and
tetanus. By inhibiting release of the neurotransmitter acetocholine,
for example, the neurotoxin produced by the bacterium Clostridium
botulinum interferes with nerve impulses and causes a
paralysis of respiratory and skeletal muscles that can cause
death. Researchers from Stanford University have now determined
the first structure of a CNT in complex with its target. The
structure at a resolution of 2.1 Å, together with enzyme
kinetic data, reveals an array of active sites (exosites)
that give the CNT its deadly specificity. Full
story.
Publication about this research: M.A.
Breidenbach and A.T. Brunger, "Substrate recognition
strategy for botulinum neurotoxin serotype A," Nature
432, 925 (2004).
Contact: Axel Brunger, Brunger@stanford.edu
Call for General
Sciences
proposals: Due July 1
The User Services Office is accepting
general user proposals from scientists who wish to conduct
research in the general sciences at the ALS during the running
period from January through June 2006. The deadline for submissions
is Friday, July 1, 2005. (This deadline does not apply to
protein crystallography proposals, which have a separate process
and schedule.) To submit a new proposal, go to the online
ALS
General User Proposal and Request for Beamtime form.
 If
you have an existing proposal for which you would like to
receive beamtime during the January through June 2006 cycle,
you must submit a Proposal Renewal Form. This new online form
replaces the ALS Experiment Report and Request for Beamtime
form. Scientists with existing proposals that are eligible
for renewal will be sent instructions on how to request a
login and password to access their proposal information and
forms. Proposals can be renewed for up to three six-month
cycles following their initial submission. After three cycles,
a new proposal must be submitted. If your proposal is designated
ALS-01186 or lower, then you must submit a new proposal.
The following resources are available
for further information:
ALS
User Services Administrator
General
user proposals
ALS online forms
Beamline
information
Proposal
scores for July–December 2005
Contact: alsproposals@lbl.gov
Subscribe to
lightsources.org
News Flash
 Keep
up to date with news from the world light-source community
by subscribing to News Flash at lightsources.org,
the Web site about and for the international light-source
community. News releases about the latest results from light-source
research are sent to your e-mail inbox. Subscribing is as
easy as filling in a few fields in an online subscription
form. All information is confidential.
Summer courses
in synchrotron-
related research
More than twenty educational opportunities,
covering all aspects of synchrotron-related research, are
available over the next several months in the US and Europe.
An up-to-date listing of the courses and facilities participating
is available at lightsources.org.
Correction to
article on
safety meeting
Last month's issue of ALSNews included
an article about a mandatory all-hands safety meeting held
at the ALS in response to a recent increase in safety incidents.
Omitted from the article was the fact that the meeting included
not only ALS staff, but all Engineering Division personnel
assigned to the ALS as well. Kem Robinson, Peter Denes, and
Alan Paterson (Engineering Division) played critical roles
in the organization and conduct of the meeting. ALSNews apologizes
for this oversight.
Note to users:
Be an
ALS booster!
 Support
for the ALS and other synchrotron light sources is highly
dependent on communicating their innovative and forefront
science. News articles in the media based on press releases
issued by your research institutions is one way to accomplish
this, provided that there is some mention of synchrotron radiation
in general and the ALS in particular in the press release
and, we hope, the news article that results. Whenever your
home institution prepares a press release based on research
that you conducted at the ALS, it would therefore be very
helpful if you would do your best to ensure that both the
ALS and synchrotron radiation are mentioned, preferably prominently
but at least somewhere. Finally, if you would notify Art Robinson
(ALRobinson@lbl.gov,
510-486-6838) at the ALS when you are aware of an impending
press release based on your research, it would also help us
in promoting your achievements and in the process ours as
well. Thank you for your cooperation.
Contact: Art Robinson, ALRobinson@lbl.gov
Selected recent
publications
We cite below a few of the more recent
publications that have been generated from work done at the
ALS.
Adams, E.J., Y.-H. Chien, and K.C. Garcia,
"Structure of a 
T cell receptor in complex with the nonclassical MHC T22,"
Science 308, 227 (2005).
Blomqvist, P., K.M. Krishnan, and H.
Ohldag, "Direct imaging of asymmetric magnetization reversal
in exchange-biased Fe/MnPd bilayers by x-ray photoemission
electron microscopy," Phys. Rev. Lett. 94,
107203 (2005).
Bradley, J., Z.R. Dai, R. Erni, N. Browning,
G. Graham, P. Weber, J. Smith, I. Hutcheon, H. Ishii, S. Bajt,
C. Floss, F. Stadermann, and S. Sanford, "An astronomical
2175 Å feature in interplanetary dust particles,"
Science 307, 244 (2005).
Ghosal, S., J.C. Hemminger, H. Bluhm,
B.S. Mun, E.L.D. Hebenstreit, G. Hetteler, D.F. Ogletree,
F.G. Requejo, and M. Salmeron, "Electron spectroscopy
of aqueous solution interfaces reveals surface enhancement
of halides," Science 307, 563
(2005).
Kim, C., N.-H. Xuong, and S.S. Taylor,
"Crystal structure of a complex between catalytic and
regulatory 
subunits of PKA," Science 307,
690 (2005).
Lee, T.T., S. Agarwalla, and R.M. Stroud,
"A unique RNA fold in the RumA-RNA-cofactor ternary complex
contributes to substrate selectivity and enzymatic function,"
Cell 120, 599 (2005).
Pierce, M.S., C.R. Buechler, L.B. Sorensen,
J.J. Turner, S.D. Kevan, E.A. Jagla, J.M. Deutsch, T. Mai,
O. Narayan, J.E. Davies, K. Liu, J. Hunter Dunn, K.M. Chesnel,
J.B. Kortright, O. Hellwig, and E.E. Fullerton, "Disorder-induced
microscopic magnetic memory," Phys. Rev. Lett.
94, 017202 (2005).
Reyes, C.L., and G. Chang, "Structure
of the ABC transporter MsbA in complex with ADP-vanadate and
lipopolysaccharide," Science 308,
1028 (2005).
Shin, S., R. El-Diwany, S. Schaffert,
E.J. Adams, K.C. Garcia, P. Pereira, and Y.-H. Chien, "Antigen
recognition determinants of
T cell receptors," Science 308,
252 (2005).
Tu, D., G. Blaha, P.B. Moore, and T.A.
Steitz, "Structures of MLSBK antibiotics bound
to mutated large ribosomal subunits provide a structural explanation
for resistance," Cell 121,
257 (2005). |
