Purification and characterization of Hb 98–114: A novel hemoglobin-derived antimicrobial peptide from the midgut of Rhipicephalus (Boophilus) microplus

► A new antimicrobial peptide was identified in the tick Ripicephalus microplus. ► This peptide is originated from bovine hemoglobin α-chain amino acids 98–114. ► Synthetic Hb 98–114 permeabilized Candida albicans cells and had fungicidal effect. ► Hb 98–114 has α-helix structure only in the presence of SDS micelles. The antimicrobial activity of hemoglobin fragments (hemocidins) has been reported in a variety of models. The cattle tick Rhipicephalus (Boophilus) microplus is a blood sucking arthropod from where the first in vivo-generated hemocidin was characterized (Hb 33–61). In the present work we identified a novel antimicrobial peptide from the midgut of fully engorged R. (B.) microplus females, which comprises the amino acids 98–114 of the alpha subunit of bovine hemoglobin, and was designated Hb 98–114. This peptide was active against several yeast and filamentous fungi, although no activity was detected against bacteria up to 50μM of the synthetic peptide. Hb 98–114 was capable of permeabilizing Candida albicans cell membrane and had a fungicidal effect against this yeast. Circular dichroism (CD) and nuclear magnetic resonance (NMR) experiments showed that Hb 98–114 has a random conformation in aqueous solution but switches to an alpha-helical conformation in the presence of sodium dodecyl sulfate (SDS). This alpha helix adopts an amphipathic structure which may be the mechanism of cell membrane permeabilization. Importantly, Hb 98–114 may play an important role in defending the tick midgut against fungal pathogens and is the first hemocidin with specific antifungal activity to be characterized.