Gelation without Attraction

By Bulbul Chakraborty

Gels are one of the most puzzling of all solids. Originally coined as a short form of gelatin, gels can be jelly-like as in Jello, or quite hard as in silica gels. They appear in suspensions of particles at extremely low volume fractions, and yet they are rigid. The conventional wisdom is that gels are a consequence of arrested phase separation of the suspended particles from the fluid. A natural mechanism for the arrest is attraction between the particles, which leads to the formation of filamentous networks of particles weaving through the suspending fluid.

Attraction has been viewed as being essential to the formation of gels. However, a new study published in Physical Review Research led by Carl Merrigan from the Chakraborty group, shows that “active particles” can gel even in the absence of physical attraction. Active matter, composed of particles that convert ambient energy to directed motion, has emerged as an important model for the collective behavior of biological matter such as bacterial suspensions. Using a combination of theoretical analysis and numerical simulations, the collaboration between the groups of Chakraborty and Shokef (Tel Aviv University) showed that the directed motion acts like an effective attraction, leading to gelation of the active particles.

The figure below shows the structure of these gels. As the particles become more active, they jam into clusters of immobile particles (red) surrounded by fluid regions (blue), and often opening up voids. Intriguingly, these active particles, which repel each other also show a transition from a dense glassy solid to a gel as the speed of directed motion is increased. The remarkable similarity between the behavior of passive particles with attraction and active particles suggests that biological entities could form solid-like aggregates without any physical or chemical attraction, purely as a consequence of their dynamics.

Reasearch image from Gelation without Attraction post

SPROUT and I-Corps Applications are Open

Sprout logoThe Brandeis Innovation SPROUT and I-Corps programs offer support for bench and non-bench research. Both programs offer funding in different amounts, mentorship, training and help in further exploring the commercial potential of inventions. SPROUT supports bench research, while I-Corps emphasizes training for both bench and non-bench researchers in developing the commercial potential of discoveries, with small grants and extensive training programs. You can apply to one or both programs.

  • If you have a technology / solution that you have started developing and you would like to get funding for it via SPROUT and/or I-Corps, then please complete this form
  • If you do not already have a technology, then you can complete this form to qualify for the I-Corps training program and be matched with a team

Icorps logo

SPROUT teams will get the chance to qualify for up to $30,000 in funding. The I-Corps program provides entrepreneurial training and covers the core of commercializing a technology or building a startup. It comes with an NSF $750 travel and training stipend and an NSF I-Corps certificate/digital badge.

Apply by February 25, 2020 at 11:59PM

Cooling Mosquitoes’ Drive for Human Blood

Drawing from Smithsonian Magazine depicting mmosquitoes and thermonter

Anopheles gambiae mosquitoes use a receptor called IR21a to navigate toward warmth, a cue that signals they’re near food (Crystal Zhu, Garrity Lab, Brandeis University).

In a recent Science paper, the Garrity lab reported that they have found an important step in how mosquitoes sense human warmth. Once found, human blood becomes a food source for the insects’ eggs. Unfortunately,  mosquito bites have, over the centuries, spread disease and misery among humans.

The lab genetically modified mosquitoes to stop expressing a molecular thermostat called IR21a in their antennae. This reduced the insects’ ability to find the heat generated by humans. The hope is that this discovery will help remove the mosquitoes temperature sensors so they don’t spread disease. This discovery has also been summarized in the Smithsonian Magazine.

Paper: Mosquito heat seeking is driven by an ancestral cooling receptor. Chloe Greppi, Willem J. Laursen, Gonzalo Budelli, Elaine C. Chang, Abigail M. Daniels, Lena van Giesen, Andrea L. Smidler, Flaminia Catteruccia, Paul A. Garrity. Science  07 Feb 2020: Vol. 367, Issue 6478, pp. 681-684.

 

 

Goode, Gelles and Kondev labs synergize in discovery of a new synergistic actin depolymerization mechanism

Shashank Shekhar, Jane Kondev, Jeff Gelles and Bruce Goode

Shashank Shekhar, Jane Kondev, Jeff Gelles and Bruce Goode

All animal and plant cells contain a highly elaborate system of filamentous protein polymers called the actin cytoskeleton, a scaffold that can be rapidly transformed to alter a cell’s shape and function. A critical step in reconfiguring this scaffold is the rapid disassembly (or turnover) of the actin filaments. But how is this achieved? It has long been known that the protein Cofilin plays a central role in this process, but it has been unclear how Cofilin achieves this feat. Cofilin can sever actin filaments into smaller fragments to promote their disassembly, but whether it also catalyzes subunit dissociation from filament ends has remained uncertain and controversial. Until now, this problem has been difficult to address because of limitations in directly observing Cofilin’s biochemical effects at filament ends. However, a new study published in Nature Communications led by postdoctoral associate Dr. Shashank Shekhar, jointly mentored by Bruce Goode, Jeff Gelles and Jane Kondev, uses microfluidics-assisted single molecule TIRF imaging to tackle the problem.

The new study shows that Cofilin and one other protein (Srv2/CAP) intimately collaborate at one end of the actin filament to accelerate subunit dissociation by over 300-fold! These are the fastest rates of actin depolymerization ever observed. Further, these results establish a new paradigm in which a protein that decorates filament sides (Cofilin) works in concert with a protein that binds to filament ends (Srv2/CAP) to produce an activity that is orders of magnitude stronger than the that of either protein alone.

Video of cofilin and Srv2/CAP collaborating

The work was funded by National Institutes of Health, National Science Foundation MRSEC and Simons Foundation grant.

MRSEC & RTI Hosts Science Outreach to Waltham Teachers

The Brandeis Materials Research Science and Engineering Center (MRSEC) and the Brandeis Research Technology and Innovation (or MakerLab) hosted a day of science and technology outreach on November 5, 2019. In the morning and for the fifth straight year, 23 Waltham High School Science teachers participated in a professional development workshop with 15 Brandeis scientists called, “Brandeis Scientists in the Classroom.” The teams of scientists and teachers visited laboratories and developed curriculum for the scientists to make future classroom visits to the High School to increase awareness of Brandeis science and to encourage WHS students to pursue STEM careers. In the afternoon, the teams were joined by more than 60 Brandeis students, staff and members of the greater community for a public event called, “Watch:City Science and Technology Forum.” This event celebrated Waltham and Brandeis as hubs of technology and discovery and promoted SciLinkR.com as a way to connect with professionals and promote science. There were short talks about public engagement with science by Waltham High School teachers Marisa Maddox and Ellen Stanton and by Brandeis scientists, Professor Avi Rodal, Dr. Anique Olivier-Mason, Dr. Vivek Vimal, and Raul Ramos. Participants also networked with each other during the poster session (20 posters by Brandeis scientists) and explored the gallery of Brandeis contributions to the Journal of Stories in Science. The organizers’ goal was for attendees to gain new perspectives in science and technology.

The event was sponsored by the Brandeis MRSEC, Research Technology & Innovation, Library, Hassenfeld Family Innovation Center, Nova BioMedical, AstraZeneca, and the New England Journal of Medicine.

 

 

 

 Basketball, Dancing Proteins, and Life-saving Drugs

Dorothee Kern, Brandeis Magazine article

Dorothee Kern (center) with students in her Brandeis lab. (Image: Mike Lovett)

The Fall 2019 issue of Brandeis Magazine features a cover story on Professor of Biochemistry and HHMI Investigator Dorothee Kern.  The article describes Kern’s trajectory from her youth and education in the former East Germany to her current research and teaching at Brandeis to her co-founding of Relay Therapeutics, a Cambridge company pioneering new approaches to anti-cancer drug discovery.

 

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