In fall 2015, ASCB awarded the first-ever ASCB-Gibco Emerging Leader Prizes to three cell biology researchers. ASCB introduced the prizes to honor not-yet-tenured independent investigators with outstanding scientific accomplishments and strong publication track records. The prizes were underwritten by Gibco, a brand of Thermo Fisher Scientific.
ASCB President Peter Walter invited each of the prize winners and each of the seven additional finalists to contribute an essay to the ASCB Newsletter. The writers were encouraged to provide a personal statement that articulates who they are, their science, and how they got into it; to describe their major scientific accomplishments; and to discuss their “dream results” and where they see themselves in the next five years.
This issue of the Newsletter features the essay of finalist Antonina Roll-Mecak.
Antonina Roll-Mecak
I was born behind the Iron Curtain, in Romania. I was a bit of a slacker in early childhood, but my extraordinary piano teacher Enikö
Antonina Roll-Mecak
National Institutes of Health
Orth taught me focus and discipline. With her, I spent much of my time, including all my summer vacations, practicing for piano competitions. While I was mesmerized by the adventures of The Microbe Hunters in Paul de Kruif’s book, my dream was to become a concert pianist. However, one cannot thrive as a pianist without touring abroad. Because of travel restrictions imposed at the time by the Romanian regime, I chose as a teen to pursue an education in the hard sciences. I had always enjoyed and been rather good at math, and I graduated with a baccalaureate in mathematics and physics.
After the Iron Curtain fell, I was awarded a full scholarship from the Cooper Union in New York City to study engineering. Serendipitously, I attended a lecture at the New York Academy of Sciences on structural biology. It was love at first sight. After a formative undergraduate internship with Ernie Mehler and Harel Weinstein at Mount Sinai, I became a graduate student at The Rockefeller University. In Stephen Burley’s laboratory, I elucidated the structures and mechanisms of the two GTPases involved in the initiation of translation in all eukaryotes.
The GTP hydrolysis–induced structural transitions that I uncovered catalyzed my interest in molecular motors and led me to postdoctoral studies in Ron Vale’s laboratory at the University of California, San Francisco. There I discovered a new microtubule-severing enzyme, spastin. Microtubule-severing enzymes perform what seems an impossible task: They break microtubules into little bits despite their considerable girth and stiffness. My structural and biochemical analyses of spastin suggested that severing enzymes might break the microtubule by pulling single tubulin molecules out of the microtubule lattice. It is hard to break a tapestry by pulling on it, but if you find a loose thread, you can unravel it with little effort. The loose threads of the microtubule are the disordered C-terminal tails of tubulin, which are pulled on by the severing enzyme.
Since starting my lab at the National Institutes of Health, I have focused on cracking the “tubulin code.” When examined through a microscope, microtubules look uniform. This is deceptive. Tubulin is extensively functionalized by a complex array of reversible posttranslational modifications, including acetylation, detyrosination, phosphorylation, glutamylation, and glycylation. These modifications vary widely among cell types, and their developmental and intracellular distribution patterns are stereotyped. This is suggestive of temporally and spatially regulated control of microtubule effectors and dynamics. Such regulation would have parallels with the histone code.
A major impediment in breaking the tubulin code has been the inability to produce “blank” tubulin and to modify it in a biochemically well-defined manner. The majority of in vitro studies are performed with tubulin purified from brain tissue. Microtubules assembled with this tubulin are mosaic and contain a randomized mixture of many tubulin isoforms and posttranslational modifications. Thus, all the topographical information encoded in microtubules by the cell has been lost or irretrievably scrambled, making the task of deciphering the tubulin code impossible. (Imagine how little we would know about gene expression if DNA were purified by first separating nucleotides and then randomly repolymerizing them!).
In my lab, we have taken a bottom-up approach to understanding tubulin modifications. We “write” the tubulin code in vitro using purified enzymes and use biophysical and cell biological techniques to uncover how the code is “read” by microtubule effectors. We have shed light on the mechanism of several of the key tubulin modification enzymes, including tubulin tyrosine ligase and the glutamylase TTLL7 as well as the tubulin acetyltransferase. We have also succeeded in generating recombinant engineered human tubulin and determined the high-resolution structure and dynamic parameters of single-isoform recombinant human neuronal microtubules, an initial step toward uncovering the biophysical correlates between tubulin sequence, structure, and dynamic instability. More recently we discovered that spastin, which is mutated in patients with hereditary spastic paraplegia, is under rheostatic control by the number of glutamates attached to the tubulin tails, demonstrating the high level of precision achievable through the tubulin code for controlling microtubule effectors.
My dream is to generate a dynamic high-resolution map of posttranslational modifications in cells and watch as it changes in real time to regulate the targeting and activity of motors and microtubule-associated proteins. When people leave my lab, I give them a daruma doll. In Japanese folk culture, a daruma is a lucky charm that is bought missing the blacks of its eyes. The user paints in one of the eyes and makes a wish. The second black eye is added when the wish is granted. My one-eyed daruma is waiting patiently on my office shelf to receive its second eye.
About the Author:
National Institutes of Health
