For Microtubule Sliding, One Arm Is Better Than Two

BPJ_113_5.c1.inddThe versatile and dynamic network of the cytoskeleton scaffold would be stagnant and lifeless if not for the tiny nanoscopic machines called molecular motors. Kinesin motors, in particular, have captured the imagination of biologists and physicists because of their ability to transform ATP into anthropomorphic walking patterns on polar microtubule filaments, which make up a significant portion of the cytoskeleton. Recent experiments have shown that kinesin motors can crosslink adjacent microtubules and facilitate sliding between them resulting in cytoplasmic streaming in Drosophila cells. This facilitates faster distribution of molecules and organelles, and determines cell-shape.

But how do motors bring about microtubule sliding? How does the collective motion of microtubules depend on the movement of motor arms? In our work, we answer these questions by studying the effect of dimeric (one active arm, one anchored arm) and tetrameric (two active arms) kinesin motors on the dynamics of confined microtubules. Through our computer simulations we find that single-armed kinesins bring about much faster dynamics in specific regions of the confinement, compared to their two-armed counterpart. This goes against the intuitive idea that more arms pull more.

The cover image for the September 5th issue of the Biophysical Journal is our rendering of filament organization for two different motor types and the effects of these differences in the large-scale structure and dynamics of confined microtubules. The green shapes on the left represent the active motor heads that walk on polar microtubules. These are depicted as a linear array of dark-blue and yellow circles. The red blob depicts the anchor belonging to the single-armed, dimeric motor. Motor arms walk in specific directions on microtubules, and stretch, producing a sliding stress between microtubules.

The structures shown in the circular confinement on top consist of sluggish filament packages formed by tetrameric motors. The arrows at the bottom represent the highly dynamic microtubule arrangement formed by dimeric motors. Here, we also depicted the trajectories that three selected microtubules have taken. The cover image was crafted to highlight the large-scale biophysical implications of seemingly trivial and counterintuitive details in biology. Through this work we emphasize the vastly different cytoskeletal dynamics due to dimeric and tetrameric motors. By way of the trajectories, we capture the active layer of microtubules close to the circular confinement we observed for the single-armed motor systems.

– Arvind Ravichandran, Gerard Vliegenthart, Guglielmo Saggiorato, Gerhard Gompper, Thorsten Auth

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BPS Members Host Another Successful Networking Event in Pennsylvania!

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The third BPS networking event in Pennsylvania, which took place on Friday, October 4, at Pennsylvania State University, was organized by William Hancock and Sheereen Majd, Pennsylvania State University. Over 125 people from 15 different institutions, some coming from as far as Syracuse University, participated in the event.

The program consisted of eight oral presentations, focusing primarily on motors, cytoskeleton, and membranes. Speakers included Lu Bai, Pennsylvania State University; David Hackney, Carnegie Mellon University; Fred Sachs, SUNY in Buffalo; Anatoly Zaytsev, University of Pennsylvania; Sethil Perumal, Pennsylvania State University; Megan McClean, Princeton University; Paul Cremer, Pennsylvania State University; and Haim Bau, University of Pennsylvania. With over 60 poster presentations, students, young faculty, and postdocs also had a chance to share their research and gain exposure.

The organizers plan on having another event at a different institution next year.

If you attended the networking event in Pennsylvania, let us know in the comments below!

Biophysical Journal Creates Virtual Collections

Have you noticed that the Biophysical Journal (BJ) this past year began releasing virtual issues, which are small collections of the best papers from selected topics that BJ publishes?

The virtual issues highlight the interdisciplinary nature of biophysics, as well as the scientific breadth and excellence of the papers published in the Journal.  All papers included in the virtual issues are freely available without a subscription under the Collections section of the BJ website.

The most recent virtual issue, Molecular Motors and the Cytoskeleton, was compiled jointly by outgoing Associate Editor Yale Goldman and incoming Associate Editor Michael Ostap. The issue highlights some of the best papers published in the Molecular Machines, Motors, and Nanoscale Biophysics section of BJ.

We asked Michael Ostap a few questions about Molecular Machines, Motors, and Nanoscale Biophysics, the subject of this Virtual Issue, and why these papers belong in Biophysical Journal.

As the field of biophysics grows ever more interdisciplinary, it also becomes increasingly inclusive. The evolution of the Journal’s Molecular Machines, Motors, and Nanoscale Biophysics section exemplifies this dynamic.  When Les Loew assumed the BJ Editor-in-Chief position in 2012, he changed the title of the section from Muscle, Motility, and Motor Proteins to its current form, which, according to Ostap, better encompasses all the research in this field.

The new title also says to researchers, “Look! We not only welcome submissions from researchers working on muscle and cytoskeletal motors, but also papers focused on the energy-transducing mechanisms of helicases, polymerases, AAA proteins, and other molecular motors.  We are also interested in the use of molecular motors, filaments and other biological macromolecules in engineered devices, and in new techniques and methods in nano-biology.”

For Ostap, molecular machines, motors, and nanoscale biophysics is about “the proteins that convert chemical energy into mechanical work.  In terms of the Biophysical Journal, I think about biophysical studies that help us gain mechanistic understanding of motor function and regulation, whether it is at the molecular, cellular, or organismal level.  Also, I think about the development of technologies that allow probing of structural dynamics, transport, mechanics, and biochemistry of single-molecules and nanoscale assemblies.”

And one of the best places for such submissions is Biophysical Journal, as exemplified by the broad range of high-impact science that investigators are submitting to this section of BJ.

The virtual issue Molecular Motors and the Cytoskeleton includes superb examples of single-molecule mechanics of molecular motors, investigations of the emergent behaviors of protein assemblies, mechanochemical models of cytoskeletal filament nucleation and mechanics, and muscle biomechanics of isolated cells and whole animals.

When asked what makes BJ the most ideal place to publish work in Molecular Machines, Motors, and Nanoscale Biophysics, Ostap explained that, “for decades, the Biophysical Journal has consistently published the research papers that have been at the foundation of the molecular motors field, and it continues to have a reputation for publishing high-quality work.  In my experience, the Editorial Board has done an excellent job providing thorough, thoughtful, and constructive reviews of papers.”

View BJ’s most recent Virtual Issue Molecular Motors and the Cytoskeleton at http://bit.ly/183rgRD.

Ross Lab Makes Microtubule Pasta on Latest BiophysJ Cover

Jennifer Ross, an author on the latest paper to be featured on the Biophysical Journal cover, describes the background of the image below. After a split lab vote, Ross submitted two very different versions of the cover, and the Journal picked this version. The paper, “Mechanical Properties of Doubly-Stabilized Microtubule Filaments,” was co-authored by Ross, Taviare L. Hawkins, David Sept, Binyam Mogessie, and Anne Straube. For more from the Ross lab, visit the website.

bpj_104_7_coverThe entire image was created using Adobe Illustrator, with online images of stovetops and kitchens as inspiration for the background. It was easy to depict the microtubules after years of making microtubule images for papers, talks, and proposals. Each component is just a shape or line, and we used some of Illustrator’s built in effects to make things look a bit more three-dimensional and cartoonish.

The image is an analog of our research published in this issue. We are working on the mechanical properties (flexibility of stiffness) of microtubule filaments. Whenever we describe filament mechanics in lectures, we also describe spaghetti because it is an everyday substance, and it actually changes its flexibility upon cooking. So, when it came time to make a cover, we automatically went to the spaghetti analogy.

In the lab, we make our measurements by determining the shape of filaments fluctuating under Brownian motion in a thin chamber. Thus, we had to have some microtubules fluctuating in a boiling pot of water. The filaments in the glass jars on the counter are different types of microtubules that have different intrinsic flexibilities, so you can see the GTPγS microtubules are bending down under gravity, but the stiff GMPCPP microtubules are rigid. We have also added proteins (Tau and MAP4), which we show as spices that can be added to the microtubule pasta. All experiments are also performed in the presence of a small molecule chemotherapeutic drug, Taxol, which we show as the tomato sauce (or “gravy” as it is called in some parts of the US) often found on pasta.

In the background, you can see our actual data results displayed as decorative tiles on the backsplash of the kitchen behind the counter and stovetop.

I have a cartoonish style of creating cover art that is clear in this cover as well as our last cover. I like to create art that incorporates the message of the science in an illustrated manner, while still portraying some of the data that we collected.

Although I don’t consider myself an artist, I also don’t think you can put boundaries between different types of creativity. Creativity can come in all forms – scientific inspiration, experimental design, and artistic expression in design or even song. Scientists are not only one thing and can have multiple passions. In fact, I think that artistic expression enhances scientific creativity. I really like that science gives me the ability and avenues to continue to be artistically creative in my talks and lectures, in my papers, and by submitting cover art, such as this.

Each paper has its own story to tell, so I cannot presume to know what that will be before we measure, analyze, write, and get new science accepted. Only nature can reveal the results that we measure, but I will definitely be there to interpret the results pictorially to the best of my abilities.

Biophysical Journal is my favorite journal – my first paper as a graduate student was in BJ and my first paper completely from my own lab was also in BJ. Getting a paper in this journal is like coming home, and I love to show my support and creativity in cover designs. I plan to hang a framed version of the cover on my office wall next to my past cover and my recent award from the Biophysical Society. I have a little shrine to biophysics in my office.

Jennifer Ross