Mol. Cells 2006; 21(2): 229~236  
A Helix-induced Oligomeric Transition of Gaegurin 4, an Antimicrobial Peptide Isolated from a Korean Frog
Su-Yong Eun, Hae-Kyung Jang, Seong-Kyu Han, Pan-Dong Ryu, Byeong-Jae Lee, Kyou-Hoon Han, Soon-Jong Kim
© The Korean Society for Molecular and Cellular Biology. All rights reserved.

Gaegurin 4 (GGN4), a novel peptide isolated from the skin of a Korean frog, Rana rugosa, has broad spec-trum antimicrobial activity. A number of amphipathic peptides closely related to GGN4 undergo a coil to he-lix 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 ana-lytical 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 α-helical structure. GGN4 induces pores in lipid membranes and, using electrophysiological meth-ods, we estimated the diameter of the pores to be exceed 7.3 ? which suggests that the minimal oligomer struc-ture responsible is a pentamer.
Keywords: Aggregation State; Analytical Ultracentrifuge; Antimicrobial Peptide; Gaegurin 4

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