Participating Students

 

Present CBI Fellows

Edward Ballister
(Mentor: Shelley Berger, Ph.D., BMB)
Supported 7/1/2009 – present

Ed is employing a “top-down” mass spectrometric method to determine the full combinatorial complement of histone modifications in yeast as they undergo the developmental program of sporulation. The goal of the studies are to identify new histone modifications that only appear during sporulation, determine whether the modifications are transient or persistent and whether they are present in combinations on the same histone or different histones. These mass spectrometric experiments will be an invaluable complement to concurrent biochemical and genetic studies on-going in the Berger lab. 

Morgan DeSantis
(Mentor: James Shorter, Ph.D., BMB )
Supported 6/1/2010 – present

I am interested in studying enzyme mechanisms. In the Shorter lab I am studying the mechanism of Hsp104, a hexameric yeast disaggregase that can dissolve amorphous aggregates and amyloids. Specifically, I am asking how Hsp104 regulates intersubunit coordination and I am studying the effects of substrate stability on the level of hydrolytic coordination

Gabriel Gonzalez
(Mentor: William DeGrado, Ph.D., BMB)
Supported 6/1/10 - present

ABC transporters are nature's most diverse protein family due to the modular design of their subunits. Gabe studies the thermodynamic and kinetic contributions of each subunit to the transport mechanism. Understanding the energetics of transport would enable the development of inhibitors to block the transport cycle and prevent tumor drug resistance, which is predominantly caused by multi-drug ABC exporters. Additionally, Gabe works on designing new substrate specificities for these transporters in order to develop custom import and export mechanisms for cell-based synthetic pathways.

Nataline Meinhardt
(Mentor: Doron Greenbaum, Ph.D., BMB)
Supported 6/1/2010 – present

In my project I am investigating the function of a human family of calcium regulated cysteine proteases called calpains through the design of highly specific inhibitors. Calpains are of biomedical interest because they have been implicated in a variety of diseases including neurodegeneration, cancer, and parasite infection. Currently, we are designing and testing novel inhibitors of calpains based on the structure of the endogenous calpain inhibitor, calpastatin. Our inhibitors mimic a two-turn alpha-helix, which binds to a unique area near the active site of calpains. This helix allows our inhibitors to be specific for calpains relative to other cysteine proteases such as the lysosomal cathepsins that do not have this helical binding pocket. We have minimized the size of the peptide relative to other calpastatin-based inhibitors by developing a novel method for stabilizing the helix of the unbound inhibitor thereby decreasing the free energy needed for binding. We have found that one inhibitor, in which the end loop of the two turn helix is stabilized, inhibits calpain 1 with a  K_i of 300 nM. We are now working to add electrophiles, such as an diketo-amide, to the N-terminus of the peptide to enhance potency through a covalent, reversible interaction with the active site cysteine. We are also performing structural studies, in collaboration with the Davies laboratory (Queen’s University) to solve the co-crystal structures of our stabilized helical peptides bound to the protease in order to better understand the molecular basis for increasing potency, selectivity and decreasing the overall size of the inhibitor.  Initially, we are using these helical inhibitors to kill malaria parasites by preventing their exit from their host human red blood cells, a process dependent on the red blood cell calpain. We hope to expand the use of these calpain inhibitors to other biological applications such as cancer.

Erin Podlesny
(Mentor: Marisa Kozlowski, Ph.D., CHEM)
Supported 9/1/2009 - present

My research focuses on the synthesis of a group of axially chiral bisanthraquinone natural products, such as skyrin or bisoranjidiol.  The reported biological activity and physical properties of some of these compounds affects a variety of public health issues including treatment of cancer (suppression of tumor cell growth), diabetes, hepatitis, depression, and use as an antioxidant.  Still, a great deal of information is lacking for the activity of many of these bisanthraquinones, citing a need for more biological studies as well as efficient stereoselective synthesis.  Specifically, the generation of the compounds will be achieved via a concerted synthesis that diverges from the same chiral bisnaphthoquinone intermediate and involves key reactions such as a copper catalyzed enatioselective oxidative biaryl coupling, oxidation/quinone formation, and tandem Diels-Alder/aromatization reactions with various vinyl ketene acetals.

Harry Schroeder, III
(Mentor: Yale Goldman, Ph.D., BMB)
Supported 9/1/2008 – present

Trey is employing single molecule studies to study switching of cargo between actin filaments (AF) and microtubles (MT), a process that is critical for appropriate endocytosis and secretion. In particular, by using an optical trap to position the cargo attached to a bead with a limited number of actively engaged motors near the actin-microtubule intersections, Trey has been able to examine cytoskeletal switching as a function of motor number. These studies reveal that the number of motors (or overall force generated) can be used to regulate switching behavior. Trey’s data also shows that rotation of the cargo is specifically seen at the intersections, which implies a torque component and suggests a mechanism for switching. Some of Trey’s work has been published in two peer-reviewed manuscripts.

Past Fellows

Julie Aaron
(Mentor: David Christianson, Ph.D., CHEM)
Supported 9/1/2006 – 8/31/2009

Cryptophanes represent an exciting class of xenon-encapsulating molecules that can be exploited as probes for nuclear magnetic resonance imaging. Julie has been working towards the targeting of these xenon-encapsulated crytophanes to a biological target.  As a model system, Julia chemically linked a xenon-encapsulated crytophane to an inhibitor of carbonic anhydrase II, a benezenesulfonamide, and determined high-resolution crystal structure of this cryptophane-derivatized benezenesulfonamide complexed with human carbonic anhydrase II. The structure of the complex reveals how an encapsulated xenon atom can be directed to a specific biological target. The crystal structure also confirms binding measurements indicating that the cryptophane cage does not strongly interact with the surface of the protein, which may enhance the sensitivity of 129Xe NMR spectroscopic measurements in solution. These studies have been a collaboration between the Christianson (Chemistry Graduate Group) and Dmochowski (Chemistry Graduate Group) laboratories and are reported in two peer-reviewed manuscripts and have implications for nuclear magnetic resonance imaging of human specimens for diagnostic purposes.

Diana Cabral
(Mentor: Barry Cooperman, Ph.D., CHEM)
Supported 9/1/2006 – 2/1/2008

Diana worked on the flourogenic labeling of tRNA molecules in order to facilitate Fluorescence Resonance Energy Transfer (FRET) experiments to study the kinetics of protein translation. Diana successfully labeled several tRNA molecules with high yield and efficiency. She collaborated with the Goldman laboratory (BMB of UPenn SOM) to use Internal Reflection Microscopy (TIRFM) to visualize immobilized ribosomes and their interaction with several labeled factors. These studies yielded novel information underlying distinct tRNA-ribosome binding events. Unfortunately, Diana decided to leave the graduate program for personal reasons so these studies are being carried forward by other members of the Cooperman and Goldman laboratories.

Daniela Fera
(Mentor: Ronen Marmorstein, Ph.D., The Wistar Institute)
Supported 9/1/2006 – 8/31/2008

Human Papillomavirus is the etilogical agent for cervical cancer that is mediated by two small viral oncoproteins, HPV-E6 and HPV-E7. Although several HPV vaccines have been developed, there is currently no therapeutic treatment for patients that already have cervical cancer. The oncogenic activity of HPV-E7 works, in part, by its ability to bind and inactivate the activity of the endogenous pRb tumor suppressor protein. Daniela has been interested in identifying and characterizing small molecule inhibitors of HPV-E7. To this end, Daniela has developed a high throughput ELISA-based screen for small molecule compounds that disrupt HPV-E7 binding to pRb, and is currently carrying out an 100,000 compound screen. In parallel, Daniela has screened 90,000 compounds in silico for HPV-E7 binding and has obtained some promising lead compounds that she is analyzing in vitro for disrupting HPV-E7-pRb binding. Daniela is also using biochemistry and crystallography to characterize the mode of HPV-E7 inhibition of the p300 histone acetyltransferase enzyme.  The ultimate goal of Daniela’s studies is to develop lead HPV-E7 compounds that might be further developed into therapeutic agents to treat cervical cancer.

Sean Mulcahy
( Mentor: Eric Meggers, Ph.D., CHEM)
Supported 9/1/2005 – 8/31/2007

Sean has been preparing organometallic compounds as novel potent and selective enzyme inhibitors. Specifically, Seann has developed a solid phase synthesis methodology to prepare a library of stable dicationic ruthenium polypridyl complexes. The idea behind his studies is that the increased coordination sphere of the metal ion would facilitate the preparation of a library of chemical entities that expand the region of synthetically accessible chemical space for the preparation of novel small molecule protein inhibitors.  Indeed, Sean has exploited this methodology to prepare a potent (IC₅₀ value in the mid nanomolar range) and selective acetylcholinesterase (AChE) inhibitor. Sean’s studies have already resulted in four peer-reviewed publications and pave the way for not only developing even more potent and selective AChE inhibitors, but also for using this methodology to develop novel potent and selective inhibitors for other protein families.

Julia Richards
(Mentor: Ivan Dmochowski, Ph.D., CHEM)
Supported 9/1/2005 – 8/31/2008

Julia has been working on the design of light responsive regulatory switches of various nucleic acid templated biological processes. Specifically, Julia has designed photoactivatable oligonucleotides whose function is blocked by a caging group until removal by irradiation. In one study, Julia designed “RNA bandages” for the photoregulation of protein synthesis in vitro and in a second study; Julia successfully designed a caged fluorescent DNA to photoregulate DNA polymerase I. Each of these studies resulted in peer-reviewed publications. Julia’s studies have implications for the temporal regulation of gene expression in living cells with possible therapeutic application.