A snapshot of the Ixodes scapularis degradome

Parasitic encoded proteases are essential to regulating interactions between parasites and their hosts and thus they represent attractive anti-parasitic druggable and/or vaccine target. We have utilized annotations of Ixodes scapularis proteases in gene bank and version 9.3 MEROPS database to compile an index of at least 233 putatively active and 150 putatively inactive protease enzymes that are encoded by the I. scapularis genome. The 233 putatively active protease homologs hereafter referred to as the degradome (the full repertoire of proteases encoded by the I. scapularis genome) represent ~1.14% of the 20485 putative I. scapularis protein content. Consistent with observations in other animals, the content of the I. scapularis degradome is ~6.0% (14/233) aspartic, ~19% (44/233) cysteine, ~40% (93/233) metallo, ~28.3% (66/233) serine and ~6.4% (15/233) threonine proteases. When scanned against other tick sequences, ~11% (25/233) of I. scapularis putatively active proteases are conserved in other tick species with ≥ 60% amino acid identity levels. The I. scapularis genome does not apparently encode for putatively inactive aspartic proteases. Of the 150 putative inactive protease homologs none are from the aspartic protease class, ~8% (12/150) are cysteine, ~58.7% (88/150) metallo, 30% (45/150) serine and ~3.3% (5/150) are threonine proteases. The I. scapularis tick genome appears to have evolutionarily lost proteolytic activity of at least 6 protease families, C56 and C64 (cysteine), M20 and M23 (metallo), S24 and S28 (serine) as revealed by a lack of the putatively active proteases in these families. The overall protease content is comparable to other organisms. However, the paucity of the S1 chymotrypsin/trypsin-like serine protease family in the I. scapularis genome where it is ~12.7% (28/233) of the degradome as opposed to ~22-48% content in other blood feeding arthropods, Pediculus humanus humanus, Anopheles gambiae, Aedes Aegypti and Culex pipiens quinquefasciatus is notable. The data is presented as a one-stop index of proteases encoded by the I. scapularis genome.