A Helix-induced Oligomeric Transition of Gaegurin 4, an Antimicrobial Peptide Isolated from a Korean Frog

  • Eun, Su-Yong (Department of Physiology, College of Medicine, Cheju National University) ;
  • Jang, Hae-Kyung (Department of Chemistry, Mokpo National University) ;
  • Han, Seong-Kyu (College of Veterinary Medicine, Seoul National University) ;
  • Ryu, Pan-Dong (College of Veterinary Medicine, Seoul National University) ;
  • Lee, Byeong-Jae (Laboratory of Molecular Genetics, Institute of Molecular Biology and Genetics, School of Biological Sciences, Seoul National University) ;
  • Han, Kyou-Hoon (Korea Research Institute of Bioscience and Biotechnology) ;
  • Kim, Soon-Jong (Department of Chemistry, Mokpo National University)
  • Received : 2005.11.01
  • Accepted : 2006.01.10
  • Published : 2006.04.30


Gaegurin 4 (GGN4), a novel peptide isolated from the skin of a Korean frog, Rana rugosa, has broad spectrum antimicrobial activity. A number of amphipathic peptides closely related to GGN4 undergo a coil to helix transition with concomitant oligomerization in lipid membranes or membrane-mimicking environments. Despite intensive study of their secondary structures, the oligomeric states of the peptides before and after the transition are not well understood. To clarify the structural basis of its antibiotic action, we used analytical ultracentrifugation to define the aggregation state of GGN4 in water, ethyl alcohol, and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). The maximum size of GGN4 in 15% HFIP corresponded to a decamer, whereas it was monomeric in buffer. The oligomeric transition is accompanied by a cooperative 9 nm blue-shift of maximum fluorescence emission and a large secondary structure change from an almost random coil to an ${\alpha}$-helical structure. GGN4 induces pores in lipid membranes and, using electrophysiological methods, we estimated the diameter of the pores to be exceed $7.3{\AA}$, which suggests that the minimal oligomer structure responsible is a pentamer.


Aggregation State;Analytical Ultracentrifuge;Antimicrobial Peptide;Gaegurin 4


Supported by : Ministry of Health & Welfare, Republic of Korea


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