Structural model of an antistasin/notch-like fusion protein from the cocoon wall of the aquatic leech, Theromyzon tessulatum

The Origin and Evolution of Antistasin-like Proteins in Leeches (Hirudinida, Clitellata)

Bloodfeeding is employed by many parasitic animals and requires specific innovations for efficient feeding. Some of these innovations are molecular features that are related to the inhibition of hemostasis. For example, bloodfeeding insects, bats, and leeches release proteins with anticoagulatory activity through their salivary secretions. The antistasin-like protein family, composed of serine protease inhibitors with one or more antistasin-like domains, is tightly linked to inhibition of hemostasis in leeches. However, this protein family has been recorded also in non-bloodfeeding invertebrates, such as cnidarians, mollusks, polychaetes, and oligochaetes. The present study aims to 1) root the antistasin-like gene tree and delimit the major orthologous groups, 2) identify potential independent origins of salivary proteins secreted by leeches, and 3) identify major changes in domain and/or motif structure within each orthologous group. Five clades containing leech antistasin-like proteins are distinguishable through rigorous phylogenetic analyses based on nine new transcriptomes and a diverse set of comparative data: the trypsin + leukocyte elastase inhibitors clade, the antistasin clade, the therostasin clade, and two additional, unnamed clades. The antistasin-like gene tree supports multiple origins of leech antistasin-like proteins due to the presence of both leech and non-leech sequences in one of the unnamed clades, but a single origin of factor Xa and trypsin + leukocyte elastase inhibitors. This is further supported by three sequence motifs that are exclusive to antistasins, the trypsin + leukocyte elastase inhibitor clade, and the therostasin clade, respectively. We discuss the implications of our findings for the evolution of this diverse family of leech anticoagulants.

Identification and functional characterization of a novel antistasin/WAP-like serine protease inhibitor from the tropical sea cucumber, Stichopus monotuberculatus

A novel antistasin/WAP-like serine protease inhibitor, named as StmAW-SPI, was identified from sea cucumber (Stichopus monotuberculatus) and functionally characterized in this study. The full-length cDNA of StmAW-SPI is 1917 bp in length with a 72 bp 5'-untranslated region (UTR), a 294 bp 3'-UTR and a 1551 bp open reading frame (ORF) encoding a protein of 516 amino acids with a deduced molecular weight of 54.56 kDa. The StmAW-SPI protein has 5-fold internal repeats (IRs) of antistasin domain and 6-fold IRs of WAP domain. For the gene structure, StmAW-SPI contains 10 exons separated by 9 introns. The StmAW-SPI mRNA expression pattern was determined using quantitative real-time PCR. The highest level of StmAW-SPI was found in the intestine, followed by coelomocytes, gonad, body wall and respiratory tree. The StmAW-SPI expressions were significantly up-regulated after polyriboinosinic polyribocytidylic acid [Poly (I:C)] or lipopolysaccharides (LPS) challenge in in vitro experiments performed in primary coelomocytes. In addition, the serine protease inhibitory activity and bacterial protease inhibitory activity of StmAW-SPI were examined, and the antibacterial activity was also demonstrated in this study. Our study, as a whole, suggested that StmAW-SPI might play a critical role in the innate immune defense of sea cucumber against microbial infections, by not only inactivating the serine protease but also inhibiting the growth of pathogens.

Surface topology and structural integrity of the Theromyzon tessulatum (Annelida: Hirudinea: Glossiphoniidae) cocoon

Cocoons secreted by the aquatic leech Theromyzon tessulatum comprise a tubular, membranous ovoid, sealed at each end by a glue-like substance, called an operculum. Scanning electron microscopy showed surface features of the T. tessulatum cocoon that included a circuitous bulge, cups that conformed to the shape of embryos, relief folds that radiated from opercula, and asymmetric distributions of protuberances on the upper aspect of the cocoon surface. The structural integrity of the T. tessulatum cocoon was assessed after exposure to a variety of denaturing conditions (e.g., extreme heat, detergents, acids). Although both the fibrous cocoon membrane and opercula were strikingly resilient, the membrane/operculum boundary appeared to be the weakest structural component of the cocoon, consistent with its functional role as an escape hatch for juvenile leeches. The operculum itself was more sensitive to denaturation than the cocoon membrane, and thus was probably the source of a major protein component isolated from the T. tessulatum cocoon (i.e., Tcp; Theromyzon cocoon protein).

Irregular helicoids in leech cocoon membranes

Helicoids in the cocoon membrane of leeches Theromyzon tessulatum and Erpobdella punctata comprise a twisted superposition of layers, each containing a variable number of planes formed by unidirectional fibrils. Straight fibrils intersecting at different angles were displayed in tangential sections through the cocoon wall of each species. When the sectioning angle was below a certain value (i.e., the critical angle), bow-shaped lines apparent in oblique sections were replaced by a succession of layers containing straight fibrils, permitting a direct measurement of step-angle change between successive layers in a helicoid. By this methodology, we determined that no regularities exist in the succession of step-angles or in layer thicknesses within the cocoon membranes, but that the distribution of step-angles between layers was unique for each cocoon type.