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In this issue:
P5 Meets at SLAC to Discuss U.S. Particle Physics Vision
Science Today: Tuning the Properties of Iron-Sulfur Clusters in Proteins
Upcoming Symposium to Celebrate Pief

SLAC Today

Thursday - February 21, 2008

P5 Meets at SLAC to Discuss U.S. Particle Physics Vision

(Image - 5 Ps)

The Particle Physics Project Prioritization Panel (P5) meets at SLAC today through Saturday in the second of three cross-country meetings to aid in forming a new 10-year plan for U.S. particle physics.

By April, P5 will make a recommendation to the U.S. High Energy Physics Advisory Panel that takes into account the field's fluid nature and considers projects in different budget scenarios.

"The panel must come up with a new vision for the field," said P5 Chair Charlie Baltay. The vision will include the high-energy physics topics that have dominated the field for the past decade as well as two extremely exciting new areas of research: neutrino physics and astrophysics. "All of a sudden, with the realization that neutrinos have mass and that the stuff we know something about makes up a lousy five percent of the universe, the field of particle physics is wide open," he said. "Our field is more intellectually exciting than it has been in recent history. Now we have to convey that excitement."

The P5 meeting at SLAC includes sessions on Super B Factories, DUSEL, Neutrino Physics, Dark Energy Experiments and Particle Astrophysics, in addition to talks on the current plans and views for research at SLAC, at Lawrence Berkeley National Laboratory and in Europe.

P5 will also host a Town Hall Meeting on Friday, February 22, at 4:30 p.m. in Panofsky Auditorium.

"We want your input into this vision," said Baltay. "I feel it's very important that SLAC remain a strong part of this field. I especially encourage the young people to come to this meeting—not just the head honchos, but also the young people who are the future of our field."

A full meeting agenda is available online.

(Daily Column - Science Today)

Tuning the Properties of Iron-Sulfur Clusters in Proteins

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. HiPIPs react oxidatively at physiological potentials, while Fds are reduced.

Sulfur K-edge x-ray absorption spectroscopy (measured at Stanford Synchrotron Radiation Laboratory Beamline 6-2) has been used to uncover the substantial influence of hydration on this variation in reactivity, in a collaborative effort led by Stanford Chemistry and Photon Science researchers. The study showed that the Fe-S covalency (a measure of the electronic overlap of the sulfur and iron orbitals forming the bonds within the clusters) is much lower in natively hydrated Fd active sites than in HiPIPs, but increases upon water removal; similarly, HiPIP covalency decreases when reversibly unfolded, exposing an otherwise hydrophobically shielded active site to water. These results demonstrate that the Fe-S covalency determined from the sulfur-K data is a direct experimental marker of the local electrostatics due to H-bonding. Studies on related model compounds and accompanying density functional theory calculations support a correlation between Fe-S covalency and ease of oxidation, which suggests that differential hydration accounts for most of the difference between Fd and HiPIP reduction potentials. This raises the intriguing possibility that oxidation/reduction potentials can be regulated by protein/protein and protein/DNA interactions that effect cluster hydration.

More information about this research is available in the full scientific highlight.

Upcoming Symposium
to Celebrate Pief

On Thursday, April 10, 2008, Stanford University will host an all-day symposium to celebrate the professional career of SLAC's founding Director, Wolfgang K.H. "Pief" Panofsky. The event will gather colleagues from SLAC, Stanford and around the world for a day of talks covering the many facets of Pief's life as a scientist, a policy maker and an arms-control advocate.

The principal venue for the event will be the Arrillaga Alumni Center on the Stanford campus, which holds 440 people. The presenters, university hosts and outside guests will attend at Arrillaga. The Panofsky Auditorium will be the secondary venue to which all presentations and discussion periods will be simultaneously broadcast.

It is very important that the event organizers know how many people will be attending at each venue so that they can avoid an overflow and can plan the logistics of coffee breaks, lunch, and so on. For this reason, please register in advance if you want to attend any or all of the lectures. When you do register, please indicate whether you will attend at the Panofsky Auditorium or at the Arrillaga Center. In addition, as is usual under such circumstances, SLAC staff will have to obtain permission from their supervisors to take time off to attend. To register for the symposium program, please visit the event website.

All registrants are welcome at the 5:30 p.m. Wine and Cheese event that closes out the day at the Arrillaga Center.

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