Download Poster

Drug Discovery and Development:
The Senna Plant and Phosphomevalonate Kinase Inhibition
Valders High School SMART Team: Corrine Brandl, Andrea Herrmann, Katarena Hubbartt, Nicole Maala, Alexandria Meidl, Hallie Reznichek
Instructor: Mr. Joseph Kinscher
Mentor: Dr. Daniel S. Sem, Marquette University
Valders High School
Abstract.
Heart disease is one of the most prominent causes of death in the United States. Hypercholesterolemia is an underlying factor leading to heart disease. By inhibiting the cholesterol synthesis pathway, scientists can develop ways to reduce the number of heart disease‐related deaths. One way could be by inhibiting the actions of phosphomevalonate kinase (PMK), a cytoplasmic enzyme found in the liver. The Valders SMART Team (Students Modeling A Research Topic), in collaboration with MSOE, built a 3D physical model of PMK. Both mevalonate 5‐phosphate (M5P) and ATP bind to the enzyme. Using ATP, PMK converts M5P to mevalonate 5‐diphosphate, a precursor to cholesterol. The inhibition of this process may be possible through a drug derived from the Indian senna plant, which is predicted to bind in place of M5P. C. Brandl
A. Herrmann
K. Hubbartt
I. Introduction
IV. A Closer Look at Cholesterol Synthesis
V. Bringing It Together
Heart disease is the leading cause of death in the United States and as such, naturally attracts the attention of persons looking to improve the lives of U.S. citizens. Developing drugs to
combat heart disease is a major focus of proteomic
researchers. One success
was the creation of statins,
but the treatment is not perfect; it may result in
side effects such as kidney
damage. For this reason, research continues into http://www.teaflavin.com/images/new_site_images/deaths.jpg
different treatment options with the intention of eliminating these concerns.
It now becomes necessary to consider the specifics of the process that cholesterol‐lowering drugs attempt to inhibit (figure 1). There is only one pathway by which cholesterol is synthesized in humans, the HMG‐CoA reductase pathway. Statins inhibit an early
step in this process. The phenolic senna compound would inhibit
a later step, the synthesis of mevalonate‐5 diphosphate
(a precursor to cholesterol) from mevalonate‐5 phosphate. Phosphomevalonate kinase is the enzyme that makes the transition possible, as it positions M5P and ATP in a way that allows for thetransfer of the γ‐phosphate on ATP to the M5P. Using nuclear magnetic resonance (NMR) technology, Dr. Daniel Sem and his lab determined that during the synthesis of mevalonate‐5 diphosphate, the ligand binding region of phosphomevalonate kinase called the “Walker A” loop oscillated at a rate of one hundred to six hundred times per second. (These data can be seen in figure 3.) The phenolic senna compound was predicted to cause the same oscillation rate, suggesting that it was likely to bind in the same manner and location in the kinase as M5P would. By binding in the same place, it would act as an effective inhibitor. Figure 1
Mevalonate 5‐Phosphate + ATP
•The chemical shift perturbation data obtained when M5P binds to PMK
II. Old Idea, New Application
N. Maala
A. Meidl
Figure 3
Researchers are exploring whether compounds extracted from the Asian senna plant, Cassia angustifolia, may be used as a
substitute to statin drugs. The senna
plant has long been used in folk remedies in Myanmar and Thailand, but has only recently attracted the attention of researchers who are looking for new drug options. http://product‐image.tradeindia.com/00239324/s/Senna‐Plant.jpg
III. Exploring the Options
H. Reznichek
J. Kinscher
Dr. Daniel Sem
Senna Phenol
Initially, the senna plant was analyzed
and nearly seven hundred compounds were identified as potential therapies (i.e. PMK inhibitors). Via computer simulation, the compounds were tested for their ability to inhibit the synthesis of
cholesterol and the top five were selected for
more thorough testing. According to computer predictions, the most likely candidate is a
phenolic compound. (As shown in the photo to the right.)
VII. Conclusion
VI. Mechanism for Phosphorylation of M5P
Mevalonate‐5 phosphate becomes mevalonate‐5 diphosphate by means of phosphorylation. This process requires the binding of two ligands, M5P and ATP, to PMK. ATP binds first, resulting in a widening of the PMK binding site. When M5P binds later, it contracts the binding site to allow γ ‐phosphate transfer to occur.
The “Walker A” loop counters these opposing charges with its high positive charge density (figure 2). A number of positively charged amino acids (such as Arginine 18, 19 and 110 and Lysine 17, 19 and 22), work to stabilize this negative charge to permit the phosphate transfer reaction to occur . There are also hinge residues that permit the two domains to move together so the reaction may occur.
In 2008, the leading cause of death in the United States was heart disease. Familial hypercholesterolemia (genetically high cholesterol) is a major factor responsible for this unfortunate statistic. Inhibiting this pathway is the purpose of cholesterol lowering drugs, such as statins. Proteomic researchers are looking into new potential drugs, such as phenolic compounds found in the senna plant, to be used instead of statins. Phenolic compounds
will hopefully inhibit the actions of phosphomevalonate kinase, (PMK),
which phosphorylates a precursor to cholesterol called mevalonate 5‐
phosphate. If proven successful, the next logical step is to develop a way to extract the necessary compound from the senna plant in an efficient manner, that would allow the drug to be readily available to those suffering from hypercholesterolemia.
Figure 2
•The chemical shift of R18 and G21 showing the Loop Motion of the “Walker A” binding Site when M5P binds to PMK VIII. References
•Functional evaluation of conserved basic residues in human phosphomevalonate kinase.
Herdendorf TJ, Miziorko HM.
Biochemistry. 2007 Oct 23;46(42):11780‐8
•Phosphomevalonate kinase: functional investigation of the recombinant human enzyme.
Herdendorf TJ, Miziorko HM.
Biochemistry. 2006 Mar 14;45(10):3235‐42.
A SMART Team project supported by the National Institutes of Health (NIH) – National Center for Research Resources Science Education Partnership Award (NCRR‐SEPA)
•NMR in drug discovery.
Pellecchia M, Sem DS, Wüthrich K.
Nat Rev Drug Discov. 2002 Mar;1(3):211‐9.
•Substrate induced structural and dynamic changes in human phosphomevalonate kinase
and implications for mechanism.
Olson AL, Yao H, Herdendorf TJ, Miziorko HM, Hannongbua S, Saparpakorn P, Cai S, Sem DS.
Proteins. 2008 Sep 17;75(1):127‐138.