Identification of novel proteases and immunomodulators in the secretions of schistosome cercariae that facilitate host entry

Comparison of cysteine peptidase activities inTrichobilharzia regentiandSchistosoma mansonicercariae

Cercariae of the bird schistosomeTrichobilharzia regentiand of the human schistosomeSchistosoma mansoniemploy proteases to invade the skin of their definitive hosts. To investigate whether a similar proteolytic mechanism is used by both species, cercarial extracts ofT. regentiandS. mansoniwere biochemically characterized, with the primary focus on cysteine peptidases. A similar pattern of cysteine peptidase activities was detected by zymography of cercarial extracts and their chromatographic fractions fromT. regentiandS. mansoni.The greatest peptidase activity was recorded in both species against the fluorogenic peptide substrate Z-Phe-Arg-AMC, commonly used to detect cathepsins B and L, and was markedly inhibited (>96%) by Z-Phe-Ala-CHN2at pH 4·5. Cysteine peptidases of 33 kDa and 33–34 kDa were identified in extracts ofT. regentiandS. mansonicercariae employing a biotinylated Clan CA cysteine peptidase-specific inhibitor (DCG-04). Finally, cercarial extracts from bothT. regentiandS. mansoniwere able to degrade native substrates present in skin (collagen II and IV, keratin) at physiological pH suggesting that cysteine peptidases are important in the pentration of host skin.

The 20S proteasome ofSchistosoma mansoni: A proteomic analysis

Proteasomes are molecular machines found in virtually all cells that provide one of the mechanisms for protein turnover. We have analysed the 20S proteasome of Schistosoma mansoni, the first multimeric complex isolated from this helminth parasite. Three chromatographic steps were employed to yield a highly homogeneous preparation. 2-DE of the purified complex revealed 58 spots, of which 46 could be assigned either an alpha or a beta proteasome signature by MS. Most of the 14 transcripts (7alpha and 7beta) encoded by the parasite genome were represented by multiple spots and we suggest that this diversity is due to PTMs of subunits. For most of the isoforms, variations in pI predominated although alterations in mass were also observed. 2-DE separations of extracts from infective cercariae and blood-dwelling adult worms probed by Western blotting, using a human anti-alpha subunit antibody, revealed different patterns of reactivity, most probably in alpha3 and alpha6 subunits, on the basis of sequence conservation. This difference was rapidly lost following transformation of the cercaria to the skin schistosomulum stage, suggesting that changes in the proteasome structure, likely caused by the introduction of a new set of PTMs, precede remodelling of the parasite body prior to intravascular migration.

Integrating transcriptome, proteome and glycome analyses of Schistosoma biology

Publication of the transcriptomes of Schistosoma mansoni and Schistosoma japonicum, in conjunction with the sequencing and assembly of their genomes, has generated a comprehensive picture of Schistosoma transcriptional and genomic diversity. Subsequently, researchers who study conjugal and developmental biology, tegumental composition and larval or egg, secretory and excretory products have used these data, in combination with the latest '-omics' technologies, to extend large-scale screens of the schistosome transcriptome, proteome and glycome. In this article, we review these postgenomic investigations and contend that the generated datasets provide a plethora of novel drug, vaccine and immunomodulatory targets that might be useful for developing new antischistosome agents.

Vaccines against the zoonotic trematodesSchistosoma japonicum,Fasciola hepaticaandFasciola gigantica

Schistosoma japonicum,Fasciola hepaticaandF. giganticaare digenetic trematodes and, therefore, possess similar life cycles. While schistosomiasis japonica has for a long time been recognised as a major disease of both humans and animals, infection with fasciolids has only been considered of relevance to animals. However, a number of recent reports indicate that fasciolosis is becoming a serious public health problem, especially in South America, Egypt and Iran (sporadic cases are also on the increase throughout Europe). Vaccines targeted at animals could play an important role in controlling these three diseases in animals and, by blocking transmission of infection, have a concurrent beneficial effect on disease in humans. Approaches towards identifying and producing vaccines against these parasites are similar and are discussed in this reveiw.

'Oming in on schistosomes: prospects and limitations for post-genomics

The recent release of version 3 of the Schistosoma mansoni genome assembly has made a wealth of information available to researchers. Here, progress made in schistosome genomics and post-genomics is considered. The current status of knowledge about the genome, transcriptome, proteome, glycome and immunome is summarized and recent publications briefly reviewed. The prospects for advances in understanding schistosome biology are highlighted. Most importantly, the limitations (which are mostly technical) that need to be addressed before the full potential of the genome database(s) can be realized are emphasized.