Lipids hit a “sweet spot” to direct cellular membrane remodeling.

14 02 2016

Lipid membrane reshaping is critical to many common cellular processes, including cargo trafficking, cell motility, and organelle biogenesis. The Rodal lab studies how dynamic membrane remodeling is achieved by the active interplay between lipids and proteins. Recent results, published in Cell Reports, demonstrate that for the membrane remodeling protein Nervous Wreck (Nwk), intramolecular autoregulation and membrane charge work together in surprising ways to restrict remodeling to a limited range of lipid compositions.

F-BAR (Fes/Cip4 homology Bin/Amphiphysin/Rvs) domain family proteins are important mediators of membrane remodeling events. The F-BAR domain forms a crescent-shaped α-helical dimer that interacts with and deforms negatively charged membrane phospholipids by assembling into higher-order scaffolds. In this paper, Kelley et al. have shown that the neuronal F-BAR protein Nwk is autoregulated by its C-terminal SH3 domains, which interact directly with the F-BAR domain to inhibit membrane binding. Until now, the dogma in the field has been that increasing concentrations of negatively charged lipids would increase Nwk membrane binding, and thus would induce membrane deformation.

Surprisingly, Kelley et al. found that autoregulation does not mediate this kind of simple “on-off” switch for membrane remodeling. Instead, increasing the concentration of negatively charged lipids increases membrane binding, but inhibits F-BAR membrane deforming activities (see below). Using a combination of in vitro assays and single particle electron microscopy, they found that the Nwk F-BAR domain efficiently assembles into higher-order structures and deforms membranes only within “sweet spot” of negative membrane charge, and that autoregulation elevates this range. The implication of this work is that autoregulation could either reduce membrane binding or promote higher-order assembly, depending on local cellular membrane composition. This study suggests a significant role for the regulation of membrane composition in remodeling.

Authors on the study included Molecular and Cell Biology graduate students Charlotte Kelley and Shiyu Wang, staff member Tania Eskin, and undergraduate Emily Messelaar ’13 from the Rodal lab; postdoctoral fellow Kangkang Song, Associate Professor of Biology Daniela Nicastro (currently at UT Southwestern), and Associate Professor of Physics Michael Hagan.



DIY your own Programmable Illumination Microscope

22 01 2016

The Fraden Group describes how to build your own Programmable Illumination Microscope in the American Journal of Physics

Have you ever marveled at the equipment used in a research lab? Have you ever wondered how a specialized piece of equipment was made? Have you ever wondered how much it would cost to build your own research microscope? Have you ever considered trying to make your own research microscope? The details on how the Fraden Group builds their Programmable Illumination Microscope for under $4000 was recently published in the American Journal of Physics.

The Programmable Illumination Microscope or PIM is a highly specialized microscope where the illumination for the sample being imaged comes from a modified commercial projector, nearly identical to the ones mounted in every classroom. For the PIM the lens that projects the image onto the screen is removed and replaced with optics (often the same lens in reverse) that shrinks the image down so that it can be focused through the microscope objective onto the sample. The light coming from the projector, which is the illumination source for the microscope, can be modified in realtime based on the image being captured by the camera. Thus the illumination is not only programmable but can also be algorithmic and provide active feedback.

This new publication in the American Journal of Physics, which is published by the American Association of Physics Teachers, is intended to help small teaching and research labs across the country develop their own PIMs to be built and used by undergraduate students. The paper includes schematics and parts lists for the hardware as well as instructions and demonstration code for the software. Any other questions can be directed to the authors Nate Tompkins and Seth Fraden.



Nature News Feature Highlights Dogic Lab Active Matter Research

6 01 2016
Click to view slideshow.

 

Biological material is constantly consuming energy to make things move, organize information such as DNA, or divide cells for reproduction; but building a fundamental theory which encompasses all of the features of biological matter is no easy task. The burgeoning field of active matter aims to understand these complex biological phenomena through physics. Active matter research has seen rapid growth over the last decade, but linking existing active matter theories with experimental tests has not been possible until recently. An explosion of biologically based and synthetic experimental systems as well as more detailed theories have arrived in recent years, and some of these foundational experiments have been conducted here at Brandeis University. Recently, a Nature News Feature (The Physics of Life) has highlighted work from Zvonimir Dogic’s lab in an article about the field of active matter and the physics which endeavors to understand biology.

 



Resolving the magnetic field around the galaxy’s central black hole

7 12 2015
Credit: M. Weiss/CfA

Credit: M. Weiss/CfA

On December 4, the journal Science (Vol. 350 no. 6265 p 1242) published a paper titled, “Resolved magnetic-field structure and variability near the event horizon of Sagittarius A*” (abstract). The paper reports that the Event Horizon Telescope has detected strong magnetic fields around the supermassive black hole at the center of the Milky Way galaxy. John Wardle, Professor of Astrophysics at Brandeis, is one of the lead authors. A co-author is Michael Kosowsky ’14, who worked on the project as a summer research project at the MIT-Haystack observatory as a junior physics major, and is now an NSF Graduate Research Fellow at Harvard.

Near a black hole, differential rotation of a magnetized accretion disk is thought to produce an instability that amplifies weak magnetic fields, driving accretion and outflow. These magnetic fields would naturally give rise to the observed synchrotron emission in galaxy cores and to the formation of relativistic jets, but no observations to date have been able to resolve the expected horizon-scale magnetic-field structure. The paper reports interferometric observations (made with antennas in Hawaii, California and Arizona) at 1.3-millimeter wavelength that spatially resolve the linearly polarized emission from the Galactic Center supermassive black hole, Sagittarius A*. We have found evidence for partially ordered magnetic fields near the event horizon, on scales of ~6 Schwarzschild radii, and we have detected and localized the intra-hour variability associated with these fields.

The above image is an artist’s impression. With the planned addition of antennas in Mexico, Chile, Europe and the South Pole, the Event Horizon Telescope will be able to make true images with angular resolution of a few tens of microarcseconds.



Eisenbud Lectures in Mathematics and Physics, October 27 – 29, 2015

27 09 2015

Eisenbud2015The Departments of Physics and Mathematics are pleased to announce that this year’s speaker for the Eisenbud Lectures in Mathematics and Physics is Jeffrey Harvey, the Enrico Fermi Distinguished Service Professor in Physics at The University of Chicago. The Eisenbud Lectures are the result of a generous donation by Leonard and Ruth-Jean Eisenbud, intended for a yearly set of lectures by an eminent physicist or mathematician working close to the interface of the two subjects.

Prof. Harvey is a leader in nonperturbative quantum field theory and string theory, known for elegant, incisive, and influential work on anomalies, solitons, and instantons; string duality; black holes in string theory; and conformal field theory for string compactifications. He was one of the members of the “Princeton String Quartet” which discovered and developed the heterotic string. He is a member of the National Academy of Sciences and the American Association for the Advancement of Science, and a Fellow of the American Physical Society. He is currently an Academic Trustee at the Institute for Advanced Study in Princeton, NJ, and a member of the Fermilab Physics Advisory Committee. These lectures promise to be enlightening and entertaining in equal measure.

The lectures will take place at Brandeis University, from October 27-29, 2015.The first lecture on Tuesday, October 27 will be a colloquium-style lecture titled “A Physicist Under The Spell of Ramanujan and Moonshine”, and will be in Abelson room 131 at 4PM; a reception will follow. The second lecture on Wednesday, October 28, “Mock Modular Forms in Mathematics and Physics”, will take place in Abelson 131 at 4PM. The final lecture, “Umbral Moonshine”, will take place in Abelson 333 at 11AM. Refreshments will be served 15 minutes prior to each talk.

We hope to see you all at what promises to be a very exciting series of talks!
— Albion Lawrence, Dept. of Physics. and Bong Lian, Dept. of Mathematics



Pairs of Supermassive Black Holes May Be Rarer Than Earlier Thought

25 09 2015
Image by David Roberts

Image by David Roberts

Recent research by David H. Roberts, William R. Kenan, Jr. Professor of Astrophysics at Brandeis, has shown that pairs of supermassive black holes at the centers of galaxies are less common than previously thought. This suggests that the level of gravitational radiation from such systems is lower than earlier predicted. This work was in collaboration with Lakshmi Saripalli and Ravi Subrahmanyan of the Raman Research Institute in Bangalore, and much of the work was done by Brandeis undergraduate students Jake Cohen and Jing Liu. It has recently been published in a pair of papers in the Astrophysical Journal Supplements and Astrophysical Journal Letters.

Gravitational waves are ripples in space-time predicted by Einstein’s 1915 General Theory of Relativity. Propagating at the speed of light, they are produced in astrophysical events such as supernovae and close binary stars.

No direct experimental evidence of the existence of gravitational waves has been found to date. We know that they exist because they sap energy from the orbits of binary systems, and using ultra-precise radio astronomy it has been shown that the changes in binary orbits of pairs of pulsars (magnetized neutron stars) are precisely as predicted by General Relativity. Hulse and Taylor were awarded the Nobel Prize in Physics for their contributions to this work.

The largest source of gravitational waves is expected to be the coalescence of pairs of supermassive black holes in the centers of large galaxies. We know today that galaxies grow by mergers, and that every galaxy harbors a massive black hole at its center, with mass roughly proportional to the galaxy’s mass. When two massive galaxies merge to form a larger galaxy, it will contain a pair of black holes instead of a single one. Through a process involving the gravitational scattering of ordinary stars the two black holes migrate toward each other and eventually coalesce into a single even more massive black hole. The process of coalescence involves “strong gravity,” that is, it occurs when the separation of the two merging black holes becomes comparable to their Schwarzschild radii. Recent developments in numerical relativity have made it possible to study the coalescence process in the computer, and predictions may be made about the details of the gravitational waves that emerge. Thus direct detection of gravitational waves will enable tests of General Relativity not achievable any other way.

In order to predict the amount of gravitational radiation present in the Universe it is necessary to estimate by other methods the rate at which massive galaxies are colliding and their black holes coalescing. One way to do this is to examine the small number of radio galaxies that have unusual morphologies that suggest that they were created by the process of a spin-flip of a supermassive black hole due to its interaction with a second supermassive black hole. These are the so-called “X-shaped radio galaxies” (“XRGs”), and a naive counting of their numbers suggests that they are about 6% of all radio galaxies. Using this and knowing the lifetime of such an odd radio structure it is possible to determine the rate at which massive galaxies are merging and their black holes coalescing.

Roberts et al. re-examined this idea, and made a critical assessment of the mechanism of formation of XRGs. It turns out that other mechanisms can easily create such odd structures, and according to their work the large majority of XRGs are not the result of black hole-black hole mergers at all. They suggest as a result that the rate of supermassive black hole mergers may have been overestimated by a factor of three to five, with the consequence that the Universe contains that much less gravitational radiation than previously believed. In fact, recent results from searches for such gravitational waves have set upper limits below previous predictions, as might expect from this work.

For more information:

 



Greater Boston Area Statistical Mechanics Meeting on Oct 24

31 08 2015

Brandeis will host the 17th annual Greater Boston Area Statistical Mechanics Meeting (GBASM) on Saturday, October 24, 2015, from 9:30-3:00. GBASM brings together researchers interested in statistical mechanics, nonlinear dynamics, condensed matter physics, biophysics, and related topics for a day-long workshop.  The meeting consists of four invited talks (30 min.), and a larger number of contributed “table talks”. The invited speakers for 2015 are:

Contributed talks will follow the format adopted the last two years. Contributors will give a brief announcement of their work in the lecture hall. We will then move to the adjacent room where each contributor will sit at a table with their laptop or tablet and discuss their research with interested participants. This format eliminates the expense associated with posters and provides greater feedback to contributors. The time preparing for a “table talk” should be similar to preparing for a short talk.

GBASM Sponsors for 2015 include the Materials Research Science and Engineering Center, Brandeis University; the Department of Physics, Boston University; the Materials Research Science and Engineering Center, Harvard University; the Department of Physics, UMASS Amherst; and the Department of Chemistry, MIT. Thanks to these subsidies, bagels, coffee, tea, and lunch will be provided at no cost if you register for GBASM by the deadline of Saturday, Oct 17.



SciFest V is in the books

9 08 2015

The Brandeis University Division of Science held its annual undergraduate research poster session SciFest V on July 30, 2015. Despite the 90 degree heat (and the steam leak) outside, the student presenter in the Shapiro Science atrium admirably kept their cool and showed off the results of their summer’s (or last year’s) worth of independent research. We had a great audience of grad students, postdocs, faculty, proud parents, members of the Brandeis senior administration, visiting neuroscientists at Brandeis helping evaluate our Computational Neuroscience training program, and physicists at Brandeis attending the IGERT Summer Institute.

IMG_1295

If you’re a student who didn’t get to present, or you’re a community member who just wanted a chance to talk about science with our energized undergrads, we’re planning another session for Fall Fest 2015. Stay tuned for details.

For a few more impressions of the event, see the story at Brandeis NOW. More pictures and abstract books are available at the SciFest site.

SciFest V by numbers

 






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