Interests and Expertise
As chemical messengers of biological information, peptides present a promising class of compounds in the preliminary stages of pharmaceutical development. Peptides are made by joining amino acids through amide bonds, giving rise to a flexible backbone with variable side chains. The large molecule is able to fold into many different three-dimensional shapes due to rotation about certain bonds; these conformations are stabilized by several molecular forces like hydrogen bonds, electrostatic attraction/repulsion and hydrophobic interactions. The same forces are involved in attracting the peptide to its target receptor, fitting like a specific key in a lock. Often, only a few parts of the molecule are responsible for binding to a receptor to cause a physiological effect, while the rest of the molecule provides a structural framework which properly orients these critical functionalities. The rational design of peptide drugs is an iterative one involving a systematic removal or modification of individual amino acids, varying chemical and physical properties such as solubility, electronic character and size and shape. This influences how the peptide can fold, which, in turn, determines its behavior. Through these structure-activity studies, the desired pharmacological action can be improved while enhancing selectivity, eliminating harmful side effects. Each peptide is designed, synthesized by solid phase peptide synthetic techniques, purified by high performance liquid chromatography and tested for bioactivity via an appropriate specialized assay. EMU students are involved in all aspects of the work.
We have applied the SAR technique to several biologically active peptides. These include the development of:
- non-addictive opiate analgesics based on deltorphin
- α-amylase enzyme inhibitors based on Tendamistat to control sugar levels in diabetes
- antimicrobial peptides based on LL-21 and Tachyplesin that destroy drug resistant bacteria
- insulin-based inhibitors of pancreatic amyloid formation in Type II Diabetes by human islet amyloid polypeptide.
Current projects are outlined below:
- Development of Antimicrobial and Anti-Cancer Peptides: Because of the increasing resistance of bacteria to traditional antibiotics, peptides with antimicrobial activity are a promising alternative to traditional therapies. Tachyplesin is an antimicrobial peptide from horseshoe crab that exhibits anti-bacterial activity by destroying bacterial cell membranes. The positive charges of the arginine and lysine residues allow for specificity for the bacterial membranes, as they are attracted to negatively charged components in the cell membranes (mammalian membranes tend to contain more positively charged phospholipids). The hydrophobic part then allows for penetration of the lipid membrane. Attraction of membrane components to the peptides disrupts membrane structure, creating holes and leading to cell death. This mechanism of action is difficult to overcome; therefore, it is believed that bacteria would not be able to develop resistance to this class of antibiotic compounds. In our analogs, the Cys residues were removed, eliminating the ability to form rings and resulting in linear peptides, which is synthetically and economically advantageous. Certain residues have been substituted to lead to better interaction with the bacterial membrane. Some of our analogs show better selectivity for bacterial over mammalian cells than the original peptide (cysteine-deleted tachyplesin, or CDT). Currently, we are investigating whether these peptides can also target and slow the growth of cancer cells in different cell lines. This is accomplished by creating/synthesizing modified peptide analogs and testing them in MTT cell viability assays, Erk signaling cascades and other analyses.
- Neuroscience projects: Using peptides to explore protein-protein interactions implicated in depression or Alzheimer's disease in vitro and in mammalian cells. In each case, the peptides are designed to mimic the sequence of a protein at the interface where it associates with another protein, whether it is an enzyme, hormone or receptor. The peptides are then assayed to determine whether they compete with the larger protein, disrupting the protein-protein interactions, coupling, or oligomerization. Structure-activity studies also can be performed by modifying the sequences (amino acid substitutions, shortening and lengthening sequences, etc.) to enhance the contacts between the peptides and the protein. Current targets include the neuroprotective peptide humanin and IGFBP3 or humanin and beta-amyloid (Alzheimer's Disease) and the D1 and D2 dopamine receptors (depression). After peptide design, synthesis and purification, assays often involve protein expression, cell culture and co-immunoprecipitations. These projects are collaborative with other chemistry faculty members.