Poster Presentation The 43rd Lorne Conference on Protein Structure and Function 2018

Ticks from diverse genera encode chemokine-inhibitory evasin proteins (#272)

Martin Stone 1 , Jenni A Hayward 1 , Julie Sanchez 1 , Andrew Perry 1 , Cheng Huang 1 , Manuel Rodriguez Valle 2 , Meritxell Canals 3 , Richard Payne 4
  1. Monash University, Clayton, VIC, Australia
  2. School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville , VIC, Australia
  3. Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, Australia
  4. School of Chemistry, University of Sydney, Sydney, NSW, Australia

Ticks are hematophagous arachnids that parasitize humans, livestock and both domestic and wild animals and often transmit viral or bacterial pathogens to their hosts. To prolong residence on their hosts, ticks secrete many salivary factors that target host defense molecules. In particular, the tick Rhipicephalus sanguineus has been shown to produce three salivary glycoproteins named ‘evasins’, which bind to host chemokines, thereby inhibiting the recruitment of leukocytes to the location of the tick bite. Using sequence similarity searches, we have identified 257 new putative evasin sequences encoded by the genomes or salivary or visceral transcriptomes of numerous hard ticks, spanning the genera Rhipicephalus, Amblyomma and Ixodes of the Ixodidae family. Nine representative sequences were successfully expressed in E. coli and eight of the nine candidates exhibited high affinity binding to human chemokines. Sequence alignments enabled classification of the evasins into two subfamilies: C8 evasins share a conserved set of eight Cys residues (four disulfide bonds), whereas C6 evasins have only three of these disulfide bonds. Most of the identified sequences contain predicted secretion leader sequences, N-linked glycosylation sites, and a putative site of tyrosine sulfation. We conclude that chemokine-binding evasin proteins are widely expressed among tick species of the Ixodidae family, are likely to play important roles in subverting host defenses, and constitute a valuable pool of anti-inflammatory proteins for potential future therapeutic applications.