Profiling of proteolytic enzymes in the gut of the tick Ixodes ricinus reveals an evolutionarily conserved network of aspartic and cysteine peptidases

Daniel Sojka¹ , Zdeněk Franta¹^,3 , Martin Horn² , Ondřej Hajdušek³ , Conor R Caffrey⁴ , Michael Mareš² and Petr Kopáček¹

¹Institute of Parasitology, Biology Centre, Academy of Sciences of the Czech Republic, České Budějovice, CZ-370 05, The Czech Republic

²Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Praha, CZ-166 10, The Czech Republic

³Faculty of Science, University of South Bohemia, České Budějovice, CZ-370 05, The Czech Republic

⁴Sandler Center for Basic Research in Parasitic Diseases, University of California San Francisco, San Francisco, CA 94158, USA

author email corresponding author email

Parasites & Vectors 2008, 1:7doi:10.1186/1756-3305-1-7


Published:	18 March 2008

Abstract

Background

Ticks are vectors for a variety of viral, bacterial and parasitic diseases in human and domestic animals. To survive and reproduce ticks feed on host blood, yet our understanding of the intestinal proteolytic machinery used to derive absorbable nutrients from the blood meal is poor. Intestinal digestive processes are limiting factors for pathogen transmission since the tick gut presents the primary site of infection. Moreover, digestive enzymes may find practical application as anti-tick vaccine targets.

Results

Using the hard tick, Ixodes ricinus, we performed a functional activity scan of the peptidase complement in gut tissue extracts that demonstrated the presence of five types of peptidases of the cysteine and aspartic classes. We followed up with genetic screens of gut-derived cDNA to identify and clone genes encoding the cysteine peptidases cathepsins B, L and C, an asparaginyl endopeptidase (legumain), and the aspartic peptidase, cathepsin D. By RT-PCR, expression of asparaginyl endopeptidase and cathepsins B and D was restricted to gut tissue and to those developmental stages feeding on blood.

Conclusion

Overall, our results demonstrate the presence of a network of cysteine and aspartic peptidases that conceivably operates to digest host blood proteins in a concerted manner. Significantly, the peptidase components of this digestive network are orthologous to those described in other parasites, including nematodes and flatworms. Accordingly, the present data and those available for other tick species support the notion of an evolutionary conservation of a cysteine/aspartic peptidase system for digestion that includes ticks, but differs from that of insects relying on serine peptidases.