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Insect Biochemistry and Molecular Biology








Hemolymph from partially fed virgin Dermacentor variabilis females was collected following Borrelia burgdorferi challenge and assayed for antimicrobial activity against Bacillus subtilis and B. burgdorferi. A small inducible cationic peptide was identified by SDS-PAGE in the hemolymph of these ticks as early as 1h post challenge. Following purification by a three-step procedure involving sequential SepPak elution, reversed phase high performance liquid chromatography (RP-HPLC) and gel electrophoresis, the yield of the active peptide was approximately 0.1% of the total protein in the hemolymph plasma. The molecular weight, 4.2kDa, was determined by MALDI-TOF mass spectrometry. N-terminal sequencing by the Edman degradation method gave a sequence for the first 30 amino acids as: G-F-G-C-P-L-N-Q-G-A-C-H-N-H-C-R-S-I-(R)-(R)-(R)-G-G-Y-C-S-Q-I-I-K. A computer search of databases showed that the peptide had 83% similarity to a defensin found in a scorpion. This is the first report of a defensin from a tick. The peptide was stable at least up to 70 degree C. Although the tick defensin alone was not immediately effective against B. burgdorferi, tick defensin plus lysozyme killed more than 65% of cultured B. burgdorferi within 1h.


NOTE: This is the author’s post-print version of a work that was published in Insect Biochemistry and Molecular Biology. The final version was published as:

Johns, R., et al. (2001). "Identification of a defensin from the hemolymph of the American dog tick, Dermacentor variabilis." Insect Biochemistry and Molecular Biology 31(9): 857-865.doi:10.1016/S0965-1748(01)00031-5

Available at: doi:10.1016/S0965-1748(01)00031-5