Ricinusin {--} a new antimicrobial peptide isolated from the hard tick \kur{Ixodes ricinus}: the third member of the tick histidine-rich defense protein family.

New gene encoding antimicrobial protein (ricinusin) was isolated from I. ricinus. The 405 nt cDNA fragment contained a 135 aa ORF, encoding a 14.5 kDa protein with 19 aa signal peptide. Gen Bank comparison of ricinusin showed weak similarity to a new type of histidine rich antimicrobial protein with unique HEAHEAHEA repeat from Boophilus microplus and Amblyomma hebraeum. The differential gene expression was strongly induced by blood feeding in larva, nymph and adults. The site of differential expression in salivary glands and gut indicates that ricinusin is induced as a part of broad-spectrum immune response. To study the amtimicrobial capacity of ricinusin and its capatibility in clearing Borrelia burgdorferi infections, it was expressed as a His-tagged fusion protein in bacterial expression system. Analysis of the genomic organization of ricinusin gene showed that it is intronless