The present invention relates to an isolated cyclic peptide, theta defensin,
having antimicrobial activity, and to theta defensin analogs. A theta defensin
can have the amino acid sequence Xaa1-Xaa2-Xaa3-Xaa4-Xaa5-Xaa1-Xaa6-Xaa4-Xaa4-Xaa1-Xaa1-Xaa6-Xaa4-Xaa5-Xaa1-Xaa3-Xaa7-Xaa5,
wherein Xaa1 to Xaa8 are defined; wherein Xaa1 can be linked through a peptide
bond to Xaa8; and wherein crosslinks can be formed between Xaa3 and Xaa3, between
Xaa5 and Xaa5, and between Xaa7 and Xaa7. For example, the invention provides a
theta defensin having the amino acid sequence Gly-Phe-Cys-Arg-Cys-Leu-Cys-Arg-Arg-Gly-Val-Cys-Arg-Cys-Ile-Cys-Thr-Arg
(SEQ ID NO:1), wherein the Gly at position 1 (Gly-1) is linked through a peptide
bond to Arg-18, and wherein disulfide bonds are present between Cys-3 and Cys-16,
between Cys-5 and Cys-14, and between Cys-7 and Cys-12. The invention also relates
to antibodies that specifically bind a theta defensin and to isolated nucleic acid
molecules encoding a theta defensin. In addition, the invention relates to methods
of using theta defensin or a theta defensin analog to reduce or inhibit microbial
growth or survival in an environment capable of sustaining microbial growth or
survival by contacting the environment with the theta defensin.
