A further insight into the sialome of the tropical bont tick, Amblyomma variegatum

Abstract

Background: Ticks--vectors of medical and veterinary importance--are themselves also significant pests. Tick salivary proteins are the result of adaptation to blood feeding and contain inhibitors of blood clotting, platelet aggregation, and angiogenesis, as well as vasodilators and immunomodulators. A previous analysis of the sialotranscriptome (from the Greek sialo, saliva) of Amblyomma variegatum is revisited in light of recent advances in tick sialomes and provides a database to perform a proteomic study.

Results: The clusterized data set has been expertly curated in light of recent reviews on tick salivary proteins, identifying many new families of tick-exclusive proteins. A proteome study using salivary gland homogenates identified 19 putative secreted proteins within a total of 211 matches.

Conclusions: The annotated sialome of A. variegatum allows its comparison to other tick sialomes, helping to consolidate an emerging pattern in the salivary composition of metastriate ticks; novel protein families were also identified. Because most of these proteins have no known function, the task of functional analysis of these proteins and the discovery of novel pharmacologically active compounds becomes possible.

Figure 1

Bootstrapped phylogram of the 12 kDa family of tick proteins. Amblyomma variegatum proteins are recognized by their Amb_var or Ambvar prefix. The remaining sequences were obtained from GenBank and have six letters (three from the genus and three from the species name) followed by their NCBI accession number. The numbers near the branches indicate the percentage bootstrap support. The bar at the bottom indicates 10% amino acid divergence.

Figure 2

Bootstrapped phylogram of the Da-p36 kDa family of metastriate tick proteins. Amblyomma variegatum proteins are recognized by their Amb_var or AMBVAR prefix. The remaining sequences were obtained from GenBank and have six letters (three from the genus and three from the species name) followed by their NCBI accession number. The numbers near the branches indicate the percentage bootstrap support (values below 50% are not shown). The bar at the bottom indicates 20% amino acid divergence. Bootstrap was performed with 1000 iterations.

Figure 3

Tick metastriate proteins containing the SMART insulin growth factor binding (IB) domain. (A) All proteins. (B) Proteins containing IB domain plus immunoglobulin (IG) and Kazal (KZ) domains. SP indicates the signal peptide region. (C) Bootstrapped phylogram of the alignment in (A). The symbols above the alignment indicate (*) identity, (:) similarity, and (.) less conserved similarity.

Figure 4

Sodium dodecyl sulfate polyacrylamide gel electrophoresis of salivary gland homogenate of Amblyomma variegatum. Lane A shows molecular mass markers, with their masses indicated in column MW. Lane B represents the tick sample. The grid at the right indicates how the gel was cut for tryptic digest of the peptides, and the two-letter-number code indicates the putative secreted proteins identified at the gel bands. The two-letter codes stand for: GR, glycine-rich protein; MT, metalloprotease; DP, dipeptidyl peptidase; CR, calreticulin; HP, hypothetical protein; CT, cytotoxin-like; and LP, lipocalin. The numbers indicate the Amb_var protein number available in Supplemental Table S2.