The Piscidins: Novel Host Defense Peptides from Fish

Mechanism of action of multi-hit host defense peptides: MolecularCotten6 basis for anti-infective and immunomodulatory properties.

  •  This ongoing project is currently funded by the National Science Foundation (MCB 1716608):

  • We investigate the direct antimicrobial and immunomodulatory properties of piscidins, host defense (antimicrobial) peptides from fish. Using methods that include CD- and NMR-monitored titrations, structural studies by SSNMR and neutron diffraction, surface plasmon (SPR), quartz crystal microbalance (QCM), calorimetry, microscopy, gel retardation assays, Ca2+-release assays, in vitro assays for determination of cytotoxicity and cell death mechanisms, and redox potential measurements, we focus on identifying the cellular targets of several isoforms and characterizing how targets are disrupted by peptides in the context of living cells and their mimics.


  • Conventionally, amphipathic antimicrobial peptides are assumed to accumulate on the anionic surfaces of bacterial and cancer cells, and act exclusively via membrane disruption and formation of stable pores. Rather, our work supports the emerging concept that anti-infective host defense peptides like piscidin use a sophisticated multi-hit mode of action, and isoforms exhibit complementary effects to target the Achilles’ heel of pathogenic cells (e.g. defensive cell walls; gene expression).


  • Our new investigations show that p1 and p3 bound to Cu act as nucleases that damage bacterial DNA, and that they work synergistically with Cu to kill biofilms and cancer cells. Specifically, the peptides use an amino terminal Cu and Ni (ATCUN) motif (XXH; X = variable residue) to mediate Cu(III)/Cu(II) redox cycles and generate ROS in the presence of Cu and co-reactants.


  • This work adds a new dimension to the long standing debate regarding how relevant the in vitro effects of host defense peptides are in vivo, and what physicochemical principles underlie them. Adopting an approach focused on the essence of the biological functions of host defense peptides in host organisms opens the door to studies revealing that host defense peptides have effects that go beyond the cell membranes of targets. This approach brings host immunity modulation and the combinatorial interplay among effector molecules back into the analysis of modes of action. It also identifies new strategies to treat drug resistant bacteria and boost host immunity.

Featured publications include:

  • M.D.J Libardo, A.A. Bahar, B. Ma, R. Fu, L.E. McCormick, J. Zhao, S.A. McCallum, R. Nussinov, D. Ren, A.M. Angeles-Boza, and M.L. Cotten. Nuclease activity gives an edge to host-defense peptide piscidin 3 over piscidin 1, rendering it more effective against persisters and biofilms. 2017. FEBS J. 284:3662-3683
  • R.M. Hayden, G.K. Goldberg,  B.M. Ferguson, M.W. Schoeneck,  M.D.J. Libardo, S.E. Mayeux, A. Shrestha, K.A. Bogardus,  J. Hammer, S. Pryshchep, H.K. Lehman, M.L. McCormick, J. Blazyk, A.M. Angeles-Boza, R. Fu, and M.L. Cotten. Complementary Effects of Host Defense Peptides Piscidin 1 and Piscidin 3 on DNA and Lipid Membranes: Biophysical Insights into Contrasting Biological Activities. 2015. J. Phys. Chem. B. 119:15235-46. We provided the first characterization of DNA/peptide aggregates by solid-state NMR and showed complementary effects between piscidin isoforms. We collaborated with groups at Hamilton College and the University of Connecticut.
  • B.S. Perrin Jr., Y. Tian, R. Fu, C.V. Grant, E.Y. Chekmenev, W.E. Wieczorek, A.E. Dao, R.M. Hayden, C.M. Burzynski, R.M. Venable, M. Sharma, S.J. Opella, R.W. Pastor, and M.L. Cotten. High-Resolution Structures and Orientations of Antimicrobial Peptides Piscidin 1 and Piscidin 3 in Fluid Bilayers Reveal Tilting, Kinking, and Bilayer Immersion. 2014. J. Am. Chem. Soc. 136: 3491–3504. Cover story, podcast, and spotlight entitled “Solid-State NMR Reveals How a Kinky Peptide Slays Microbes”. We solved the first high resolution structures of alpha-helical host defense peptides bound to fluid bilayers and deposited them in the Protein Data Bank. This work featured a collaboration with Dr. Rich Pastor at the NIH.
  • R. Fu, E.D. Gordon, D.J. Hibbard, and M. Cotten. High resolution heteronuclear correlation NMR spectroscopy of an aligned antimicrobial peptide: Direct evidence of spectral enhancement at high magnetic field and peptide-water interactions at the water-bilayer interface. 2009. J. Am. Chem. Soc. 131: 10830–10831. We collected NMR data on state-of-the-art instruments, including the 900 MHz ultra-wide bore spectrometer at the National High Magnetic Field Laboratory, and helped develop new solid-state NMR methodology for membrane-bound species. These experiments were done in collaboration with Dr. Riqiang Fu at the NHMFL.