Trimethoprim decorated beads for magnetically manipulating mammalian cells

Brandeis grad students Yue Pan (Chemistry) and Marcus Long (Biochemistry), together with postdoc Hsin-Chieh Lin and Professors Lizbeth Hedstrom and Bing Xu, have extended their previous work on 6 nm diameter magnetic nanobeads (comparable in size to a globular protein). They’ve shown that when decorated with the ligand trimethoprim, the nanobeads can be used to selectively bind to target E coli DHFR fusion proteins, and in addition can be used to manipulate live cells with a magnetic force. This work entitled “Cell Compatible Trimethoprim (TMP)-Decorated Iron Oxide Nanoparticles Bind Dihydrofolate Reductase (DHFR) for Magnetically Modulating Focal Adhesion of Mammalian Cells” is now online in the Journal of the American Chemical Society (JACS).

These small, magnetic beads are the first example of solid supported trimethoprim and have numerous advantages over larger traditional beads, including rapid purification, and ultra low non-specific binding. It is, however, their ability to affect live cells that is most important. In the paper they first show that Cos-1 and HeLa cells can be incubated with the beads for over 5 days with little cell death. These cells can subsequently be manipulated by transfection. Finally when exposed to a magnetic force, the focal adhesion of bead-treated Cos-1 cells can be manipulated.

See also: recommendation at Faculty of 1000

A lattice of interacting chemical oscillators

At Brandeis, there is a long tradition of interesting experiments on the Belousov-Zhabostinsky reaction system, with the legendary Zhabotinsky himself having been a part of the fraternity. This reaction system shows interesting oscillatory and stable patterns (see videos on Youtube). In the Fraden lab, an oil emulsion of micron-sized water droplets containing the BZ reactions, was shown to show interesting synchronization properties and complex spatial patterns [Toiya et al, J. Phys. Chem. Lett. 1, 1241 (2010)]. A coupling between the droplets due to preferential diffusion of an inhibitory reactant (bromine) in the oil medium was seen to be responsible for these collective phenomena.

In a new paper titled “Phase and frequency entrainment in locally coupled phase oscillators with repulsive interactions” in Phys. Rev. E, Physics Ph. D student Michael Giver, postdoc Zahera Jabeen and Prof. Bulbul Chakraborty show that neighboring oscillators can be modeled as Kuramoto phase oscillators, coupled nonlinearly to its nearest neighbors. The form of the coupling chosen is repulsive, which favors out of phase synchronization. They show using linear stability analysis as well as numerical study that the stable phase patterns depend on the geometry of the lattice. A linear chain of these repulsively coupled oscillators shows anti-phase synchronization, in which neighboring oscillators show a phase difference of π The phase difference between the neighboring oscillators when placed on a ring however depends on the number of oscillators. In such a case, the locally preferred phase difference of π is ruled out for an odd number of oscillators, as this may lead to frustration. When these oscillators are placed on a triangular lattice in two dimensions, the geometry of the lattice constrains the phase difference between two neighboring oscillators to 2 π /3. Interestingly, domains with different helicities form in the lattice. In each domain, the phases of any three neighboring oscillators can vary continuously in either clockwise or an anti-clockwise direction. Hence, phase difference between the nearest neighbors are seen to be ±2π /3 in the two domains (See figure). A phase difference of π is seen at the interfaces of these domains. These domains can grow in time, resembling domain coarsening in other statistical studies. At large coupling strengths, the domains freeze in size due to frequency synchronization of all the oscillators. Hence, an interplay between frequency synchronization and phase synchronization was seen in this system. Ongoing studies in the BZ experimental setup at the Fraden Lab, find correlations with the above results. Hence, insights into a complex system like the BZ oscillators could be gained using the phase oscillator formalism.

The research was supported by the ACS Petroleum Research Fund and the Brandeis MRSEC. Michael Giver is a trainee in the Brandeis NSF-sponsored IGERT program Time, Space & Structure: Physics and Chemistry of BIological Systems

Sprout Grant Winners 2011

Entrepreneurship is alive and well at Brandeis.

Last week, fourteen teams of Brandeis scientists presented their research to a panel of industry experts to compete for funding from the Brandeis University Virtual Incubator Sprout Grant Program.  The Virtual Incubator seeks to nurture and support entrepreneurial scientists at Brandeis by providing education, mentoring, networking and seed grants to help move their discoveries from the laboratory to the market.

Judges were impressed by the team presentations. The teams ranged from biologists who have projects that could be ready for licensing as early as next year, to computer science / IT entrepreneurship students with a web application that already has 1200 users.

“We were overwhelmed by the phenomenal proposals we received” says Irene Abrams, Associate Provost for Innovation.  “The response was incredible – with only a few weeks notice, 23 teams applied for Sprout Grants and 14 presented their proposals to the panel of judges.  I was impressed by the level of creativity among the applicants, and by the hard work the teams put into the presentations.  We only had $50,000, so we had to turn down many excellent applications, which we would have funded if we had more money.”

The 2011 winning projects are:

  • Generation Of A Rapid And Efficient Protein Knockout System, Lead Scientist:  Erin Jonasson (with Satoshi Yoshida)
  • Identification Of Molecules For Stabilizing DJ-1, A Protein Involved In Parkinson And Alzheimer Diseases. Lead Scientist: Joey Salisbury (with Brian Williams, Ala Nassar, Jeff Agar and Greg Petsko)
  • Targeting Oncogenic Ras For Protein Degradation, A Novel Approach To Therapy. Lead Scientist: Rory Coffey (with Marcus Long, Ruibao Ren, and Liz Hedstrom)
  • Identifying Pharmacological Chaperones that Promote Survival in Mouse Models of ALS, Lead Scientist: Jared Auclair (with Joey Salisbury, Dagmar Ringe, Greg Petsko, and Jeff Agar)
  • A Novel, Low Cost, Highly Sensitive Form Of Suppression PCR, Lead Scientist: Ken Sugino (with Sean O’Toole and Sacha Nelson)
  • Zen.Do, Team: Bill DeRusha, Joshua Silverman, Jason Urton (Computer Science)

see also: Brandeis NOW

Physics students present research at 20th Annual Berko Symposium on May 16

On Monday, May 16, the Physics Department will hold the Twentieth Annual Student Research Symposium in Memory of Professor Stephan Berko in Abelson 131. The symposium will end with talks by the two Berko Prize winning students, undergraduate Netta Engelhardt and graduate student Tim Sanchez. The whole department then gathers for a lunch of cold cuts, cookies and conversation. “It’s a great way to close out the academic year,” said Professor of Astrophysics and Department Chair John Wardle. “We come together to celebrate our students’ research and hear what the different research groups are doing.”

The undergraduate speakers will describe their senior thesis honors research. This is the final step in gaining an honors degree in physics, and most of them will also be co-authors on a paper published in a mainline science journal. The graduate student speakers are in the middle of their PhD research, and will disucss their progress and their goals.

The prize winners are nominated and chosen by the faculty for making particularly noteworthy progress in their research. Graduate student winner Sanchez’ talk is titled “Reconstructing cilia beating from the ground up.” He works in Professor Zvonimir Dogic’s lab studying soft condensed matter. Undergraduate winner Engelhardt’s talk is titled “A New Approach to Solving the Hermitian Yang-Mills Equations”. She works with Professors Matt Headrick and Bong Lian (Math) on problems in theoretical physics and string theory. The schedule for Monday morning and abstracts of all the talks can be found on the Physics Department website.

Sanchez’ research very much represents the growing interdisciplinary nature of science at Brandeis. Here, a physicist’s approach is used to study a biological organism. Professor Zvonimir Dogic says of his work “He has made a whole series of important discoveries that are going to have a measurable impact on a number of diverse fields ranging from cell biology, biophysics, soft matter physics and non-equilibrium statistical mechanics.  His discoveries have fundamentally transformed the direction of my laboratory and probably of many other laboratories as well.”

Engelhardt’s research is much more abstract and mathematical, and concerns fundamental problems in string theory, not usually an area tackled by undergraduates. Professor Headrick says “Netta really, really wants to be a theoretical physicist, preferably a string theorist. She has a passion for mathematics, physics, and the connections between them.” He adds that she is utterly fearless in tackling hard problems. Netta has been awarded an NSF Graduate Research Fellowship based on her undergraduate work here.  Next year she will enter graduate school at UC Santa Barbara and will likely work with eminent string theorist Gary Horowitz, who has already supervised the PhD research of two other Brandeis physics alumni, Matthew Roberts ’05, and Benson Way ’08.

This Student Research Symposium is now in its 20th year. The “First Annual…..” (two words which are always unwise to put next to each other) was initiated in 1992 by Wardle to honor Professor Stephan Berko, who had died suddenly the previous year. Family, friends and colleagues contributed to a fund to support and celebrate student research in his memory. This provides the prize money which Netta and Tim will share.

Stephan Berko was a brilliant and volatile experimental physicist who was one of the founding members of the physics department. He was born in Romania in 1924 and was a survivor of both the Auschwitz and Dachau concentration camps. He came to the United States under a Hillel Foundation scholarship and obtained his PhD at the University of Virginia. He came to Brandeis in 1961 to establish a program in experimental physics and worked tirelessly to build up the department. Together with Professors Karl Canter (dec. 2006) and Alan Mills (now at UC Riverside) he established Brandeis as a world center for research into positrons (the anti-matter mirror image of ordinary electrons). In a series of brilliant experiments they achieved many “firsts,” culminating in election to the National Academy of Sciences for Steve, and, it has been rumored, in a Nobel Prize nomination for the three of them. Steve was as passionate about teaching as he was about research, and when he died, it seemed most appropriate to honor his memory by celebrating the research of our graduate and undergraduate students. During the coffee break on Monday, we will show a movie of Steve lecturing on “cold fusion,” a headline-grabbing but phony claim for producing cheap energy from 1989.

Mapping hydrogens in chymotrypsin structures with neutron diffraction

In a new paper “Time-of-flight neutron diffraction study of bovine γ-chymotrypsin at the Protein Crystallography Station” published in this month’s edition of the journal Acta Cryst F, Biochemistry grad student Louis Lazar and co-workers from the Petsko-Ringe lab report progress on their project to determine exact hydrogen positions in proteins using neutron diffraction.

Neutron diffraction was chosen, as opposed to X-ray diffraction, because one can visualize hydrogen species directly using neutrons, while it is extremely difficult and in most cases impossible to do so using X-ray diffraction. They chose the protein γ-chymotrypsin in order to determine hydrogen positions, as it fills the necessary requirements to be suitable for a neutron diffraction experiment. These requirements include a very large crystal size (> 1 mm3), moderately sized unit cell axes (no dimension greater than 100 Å), and it must be very stable as well as well-characterized. γ-chymotrypsin is the stereotypical serine protease, cleaving C-terminal to aliphatic and aromatic residues and containing a catalytic triad of serine, histidine, and aspartate. This information on hydrogen placement can then be applied to improve computational methods in which said placement is paramount, such as molecular modeling and rational drug design.

The paper details the collection of neutron data at pD (pH*) 7.1, with the help of the scientists at the Los Alamos National Laboratory. In particular, from the initial maps, they note that the catalytic histidine is doubly protonated, while the serine and aspartate making up the catalytic triad do not show density for the presence of deuterium. In order to complete the study of γ-chymotrypsin, data at a variety of pH values must be collected; data at pD (pH*) 5.6 has already been collected (Acta Cryst F65, 317-320), and data at pD (pH*) 9.0 will be collected in the future.

see also: full text of article (Brandeis users)

A molecular function of Zillion Different Screens protein explained

In a recent paper in Journal of Cell Biology entitled “Spatial regulation of Cdc55-PP2A by Zds1/Zds2 controls mitotic entry and mitotic exit in budding yeast“, Brandeis postdoctoral fellow Valentina Rossio and Assistant Professor of Biology Satoshi Yoshida reveal a molecular function of a mysterious protein Zds1.

The Zds1 protein in yeast  was identified some years ago in “a zillion different screens” for cell cycle mutants, stress response mutants, RNA metabolism mutants, etc., but the molecular function of the protein remained a mystery for more than 15 years. Rossio revealed that Zds1’s key target is a protein phosphatase 2A (PP2A) complex. She showed that Zds1 controls nucleocytoplasmic distribution of PP2A complex, and that this regulation is critical for cells to know when to enter and to exit from mitosis (picture below; cells lacking Zds proteins adopt an abnormal shape because of problems in mitosis). Rossio thinks all the other complicated phenotypes associated with ZDS1 can also be explained by PP2A regulation and is currently studying mechanistic details about the Zds1-PP2A interaction.

See also the accompanying commentary “Proteins keep Cdc55 in its place

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