Professor Tess Moon's graduate students (l-r) Jonathan L. Gaspredes, Talal E. AlOtaibi and Steven Kreuzer are studying forces on proteins in order to better understand normal cellular processes.
For the 2011-2012 academic year, Professor Tess Moon in the Department of Mechanical Engineering at The University of Texas at Austin, received a Moncrief Grand Challenge Faculty Award to study ways physiologically relevant mechanical loads (i.e. forces or displacements) are carried in proteins. Tess Moon and her students in the IMPACT Laboratory are studying the effects of mechanical forces on proteins, key components in living cells and tissues, in order to better understand their relationships to normal cellular processes, as well as to the progression of disease.
Professor Moon explains:
"Cells cannot live without attachments to other cells. If they lose that attachment, they will die. This research studies part of that attachment, and has potential applications into slowing or stopping the spread of disease such as cancer, osteoporosis and osteoarthritis at contact points between individual cells."
In this video, Ph.D. student, Steven Kreuzer, explains the research using easy-to-understand language, a model they constructed, and a balloon. View video in larger format on YouTube.
Read the transcript.
Virtually all cells in the body have forces that they act on or against. When muscles stretch or contract, a heart beats, or blood flows through an artery or vein, forces are exerted on the cells. In this research the team exerts artificial forces on cells at the molecular level and studies the responses of different proteins to varying loads or forces. Please view the video where Steven Kreuzer uses easy-to-understand demonstrations of the team's research.
Professor Tess Moon, Ph.D., candidate Steven M. Kreuzer, along with M.S. candidates Talal E. AlOtaibi and Jonathan L. Gaspredes, all from the Department of Mechanical Engineering at The University of Texas at Austin, are collaborating with Dr. Ron Elber, W.A. "Tex" Moncrief Chair in Computational Life Sciences and Biology in the Department of Chemistry and Biochemistry on this research.
Alpha helix at the secondary structure level of a protein molecule. Hydrogen bonds are shown with yellow dots. This is the section of a protein that Steven Kreuzer is studying.
The image on the left illustrates the secondary structures comprised of amino acids in a cell found inside an alpha helix protein structure (secondary level structure). When the cell is functioning correctly, these structures fit together, not unlike a three-dimensional puzzle (see the secondary, tertiary and quaternary structure diagram above). Under loads (for example, forces or displacements), they begin to unfold, and the protein no longer works properly. In this research, they will look at what happens when small sections of the protein unfold. They will unfold one loop of an alpha helix protein at a time, to see how the amino acids in each loop are affected by varying loads. They will not completely disable all functionality, but disable only very specific transmission functions.
Previous Related Research
Research in this field has been overwhelmingly focused on understanding extreme cases of failure in which proteins are violently destroyed. The behavior of these fundamental secondary structures under sub-failure loads is being studied to better understand protein load carrying at levels physiologically relevant to essential cellular processes.
Moon's, Elber's and Kreuzer's Research on Mechanical Forces at the Cellular Level
Mechanical forces play a vital role in regulating fundamental cellular processes. In addition to their well-recognized role in muscle contraction, mechanical forces power and regulate many other essential cellular processes such as:
- migration in wound healing and cancer metastasis
- proliferation in bone growth and tissue remodeling
- differentiation in embryonic and adult stem cells
- regulation of signaling pathways.
Insights gained from these investigations into load carrying of protein secondary structures will provide a means for interpreting biological functioning of many diverse proteins. Ultimately a clear description of load carrying within protein building blocks will allow for clearer interpretation of more difficult problems in which complex, multi-unit proteins and multi-protein structures are simulated under load. Additionally, as protein unfolding is a primary means to understand the energetics of the formation of proteins, these results will provide critical insight into protein folding with broad application to a variety of fields, including bioinformatics.
Separately, Dr. Moon received a three-year grant, beginning September 2011, from the Biomedical Engineering Program of the National Science Foundation's Directorate of Engineering to study how applied loads—even those in the sub-unfolding regime—can significantly perturb a protein from its native form and chemical behavior. The program is devoted to studying Focal Adhesion Kinase (FAK), a molecule with a fundamental role in communication between the exterior and interior of a cell. As FAK underlies the cell's membrane, it may play a role in mechanotransduction: the transfer of a mechanical signal (such as a molecular stretch) into a chemical communication.
Molecular dynamics of FAK molecules
FAK protein molecules are one-thousandth the size of a human hair, so direct experimental observation of their behavior is nearly impossible. Thus, in order to study these fundamental processes of mechanotransduction through proteins, it is necessary to perform computational experiments in which their behavior is studied at an atomic resolution in a process referred to as "molecular dynamics."
Tracking the motion of individual atoms of FAK proteins under various conditions
Using the vast super-computing resources available at the Texas Advanced Computing Center (TACC), molecular dynamics simulations track the motion of these proteins under various mechanical conditions. Analysis of the vibrations and shape changes of the molecules allow Dr. Moon and her students to understand how mechanotransduction can result from altered protein motion under load.
How FAK binds to and communicates with other proteins
Schematic of load carried through the focal adhesion kinase (FAK) layer of an animal cell and the molecular structure of the exterior cell wall.
Many cells bind to components of the extracellular matrix (ECM) a complex, insoluble, cellular network framework. Cell adhesion can occur by focal adhesions, large, mechanical linkage proteins that connect the ECM to actin filaments of the cell. This cell-to-ECM adhesion is regulated by specific cell surface cellular adhesion molecules (CAM) known as integrins. Integrins are cell surface proteins that bind cells to ECM structures.
Mechanotransduction involves the translation of physical forces on the exterior of a cell (bottom) being transmitted through the cell membrane into the interior (top) and, ultimately, conversion of these forces into a chemical signal. FAK (middle, orange) is one of the primary players in mechanotransduction, coordinating the response of focal adhesions to applied loads. Despite its well-known importance, the means by which FAK performs the force-to-signal conversion is largely unknown and a primary subject of Dr. Moon's research.
Dr. Moon, Steven Kreuzer, Talal E. AlOtaibi and Jonathan L. Gaspredes are using molecular dynamic simulations to study the behavior of secondary structures and their interactions to understand FAK's response to load. Two of FAK's fundamental processes are examined, including the ability of the molecule to competently bind to other load-carrying proteins, as well as FAK's ability to become activated, and thereby chemically regulate other molecules within the cell. Competent binding of FAK to other molecules requires that forces carried by these partner proteins are not in excess of the strength of FAK, allowing FAK to retain its shape without unfolding. Activation of the communication behavior of FAK may be a result of applied loads causing a change of shape of the molecule to expose an otherwise inaccessible site within FAK that can signal with other molecules.
The study of FAK's mechanical properties are aided by a collaboration with the experimental codiscoverer of FAK, Dr. Michael Schaller, Chair of the Department of Biochemistry at West Virginia University's School of Medicine, in which biochemical and mutational studies are complemented by single molecule mechanical experiments performed at The University of Texas at Austin, providing a means to experimentally verify computational observations.
Identifying molecular targets for treatment of a variety of diseases
Knowing load's effect on proteins may help identify molecular "targets" or small molecules for therapeutic treatments for a wide variety of diseases. For example, as a key regulator of processes central to tumorigenesis (tumor formation), metastasis (the spreading or transmission of cancerous cells) and intra and intra cell signaling, FAK is a potential target for anti-cancer drugs. But, FAK targeting requires finesse as systemic FAK inhibition may have severe side effects, given it is found in virtually every cell and plays a critical role in mediating signaling pathways vital to normal cellular processes. Insights harnessed will help identify viable, perhaps even mechanically induced, targets—or small molecules—for therapy specifically designed to avoid systemic issues associated with complete "knock-out" of FAK.
Contact Information
For additional information on this research, please contact Dr. Tess Moon or
