Disintegrins from hematophagous sources

Abstract

Bloodsucking arthropods are a rich source of salivary molecules (sialogenins) which inhibit platelet aggregation, neutrophil function and angiogenesis. Here we review the literature on salivary disintegrins and their targets. Disintegrins were first discovered in snake venoms, and were instrumental in our understanding of integrin function and also for the development of anti-thrombotic drugs. In hematophagous animals, most disintegrins described so far have been discovered in the salivary gland of ticks and leeches. A limited number have also been found in hookworms and horseflies, and none identified in mosquitoes or sand flies. The vast majority of salivary disintegrins reported display a RGD motif and were described as platelet aggregation inhibitors, and few others as negative modulator of neutrophil or endothelial cell functions. This notably low number of reported disintegrins is certainly an underestimation of the actual complexity of this family of proteins in hematophagous secretions. Therefore an algorithm was created in order to identify the tripeptide motifs RGD, KGD, VGD, MLD, KTS, RTS, WGD, or RED (flanked by cysteines) in sialogenins deposited in GenBank database. The search included sequences from various blood-sucking animals such as ticks (e.g., Ixodes sp., Argas sp., Rhipicephalus sp., Amblyommasp.), tabanids (e.g., Tabanus sp.), bugs (e.g., Triatoma sp., Rhodnius prolixus), mosquitoes (e.g., Anopheles sp., Aedes sp., Culex sp.), sand flies (e.g., Lutzomyia sp., Phlebotomus sp.), leeches (e.g., Macrobdella sp., Placobdella sp.) and worms (e.g., Ancylostoma sp.). This approach allowed the identification of a remarkably high number of novel putative sialogenins with tripeptide motifs typical of disintegrins (>450 sequences) whose biological activity remains to be verified. This database is accessible online as a hyperlinked worksheet and displays biochemical, taxonomic, and gene ontology aspects for each putative disintegrin. It is also freely available for download (right click with the mouse) at links http://exon.niaid.nih.gov/transcriptome/RGD/RGD-Peps-WEB.xlsx (web version) and http://exon.niaid.nih.gov/transcriptome/RGD/RGD-sialogenins.zip (stand alone version).

Keywords: angiogenesis; bloodsucking; disintegrins; hematophagy; platelet aggregation; proteome; salivary; sialogenins; sialome; snake venom; thrombus; transcriptome.

Figure 1

ClustalW alignment for putative VGD disintegrins from Triatominae.

Figure 2

Clustal alignment for putative KGD (A and B) and MLD (C) disintegrins from Triatominae. (D) Neighbor-joining phylogram for the sequences presented in A–C, and Figure 1. The numbers in the phylogram nodes indicate percent bootstrap support for the phylogeny. The bar at the bottom indicates 20% amino acid divergence in the sequences.

Figure 3

ClustalW alignment for putative KGD (A), and RGD (B and C) disintegrins from Metastriate ticks.

Figure 4

ClustalW alignment for putative KTS (A) disintegrins from Amblyomma sp. Ticks;(B) phylogenetic tree for the sequences presented in A and from other KGD or RGD disintegrins from other metastriates (alignment not shown).

Figure 5

ClustalW alignment for putative RGD (A), and RGD (B and C) disintegrins from Ixodidae ticks.

Figure 6

ClustalW alignment for putative VGD (A) and RTS (B) disintegrins from Ixodidae ticks.

Figure 7

Neighbor-joining phylogram for the Ixodidae sequences presented in Figure 5 and Figure 6. The numbers in the phylogram nodes indicate percent bootstrap support for the phylogeny. The bar at the bottom indicates 20% amino acid divergence in the sequences.

Figure 8

ClustalW alignment for putative RGD (A) and K/RGD disintegrins; (B) from Ornithodoros ticks. C, Neighbor-joining phylogram for the Ixodidae sequences presented in (A) and (B). The numbers in the phylogram nodes indicate percent bootstrap support for the phylogeny. The bar at the bottom indicates 20% amino acid divergence in the sequences. The sequences of other known disintegrins (e.g., disagregin, savignygrin, monogrin) in addition to monobin (a thrombin inhibitor with RGD) [38] have also been included.

Figure 9

ClustalW alignment for putative WGD, KGD and VGD disintegrins from the rat flea Xenopsylla cheopis.