Trypsin- and Chymotrypsin-Like Serine Proteases in Schistosoma mansoni – ‘The Undiscovered Country’

Abstract

BackgroundBlood flukes (Schistosoma spp.) are parasites that can survive for years or decades in the vasculature of permissive mammalian hosts, including humans. Proteolytic enzymes (proteases) are crucial for successful parasitism, including aspects of invasion, maturation and reproduction. Most attention has focused on the ‘cercarial elastase’ serine proteases that facilitate skin invasion by infective schistosome larvae, and the cysteine and aspartic proteases that worms use to digest the blood meal. Apart from the cercarial elastases, information regarding other S. mansoni serine proteases (SmSPs) is limited. To address this, we investigated SmSPs using genomic, transcriptomic, phylogenetic and functional proteomic approaches.Methodology/Principal FindingsGenes encoding five distinct SmSPs, termed SmSP1 - SmSP5, some of which comprise disparate protein domains, were retrieved from the S. mansoni genome database and annotated. Reverse transcription quantitative PCR (RT- qPCR) in various schistosome developmental stages indicated complex expression patterns for SmSPs, including their constituent protein domains. SmSP2 stood apart as being massively expressed in schistosomula and adult stages. Phylogenetic analysis segregated SmSPs into diverse clusters of family S1 proteases. SmSP1 to SmSP4 are trypsin-like proteases, whereas SmSP5 is chymotrypsin-like. In agreement, trypsin-like activities were shown to predominate in eggs, schistosomula and adults using peptidyl fluorogenic substrates. SmSP5 is particularly novel in the phylogenetics of family S1 schistosome proteases, as it is part of a cluster of sequences that fill a gap between the highly divergent cercarial elastases and other family S1 proteases.Conclusions/SignificanceOur series of post-genomics analyses clarifies the complexity of schistosome family S1 serine proteases and highlights their interrelationships, including the cercarial elastases and, not least, the identification of a ‘missing-link’ protease cluster, represented by SmSP5. A framework is now in place to guide the characterization of individual proteases, their stage-specific expression and their contributions to parasitism, in particular, their possible modulation of host physiology.

Excretion/secretion products from Schistosoma mansoni adults, eggs and schistosomula have unique peptidase specificity profiles

“…Generally, trypsin-like serine peptidases cleave peptides with these P1-amino acids equally well. These data support our previous finding that a number of different trypsin peptidases are expressed in adult S. mansoni [19]. In addition, a second serine peptidase activity is present that has chymotrypsin-like P1 specificity for Trp.…”

“…The proteolytic profile of schistosomular ES products is the simplest measured and centers on a single or predominant serine peptidase with a strict P1- P1’ specificity for charged amino acids and only minor amino acid engagements at the other prime and non-prime binding sites. The activity may be due to one or more of a number of schistosomular serine peptidases we previously measured by both gene expression profiling and functional activity analyses with small peptidyl substrates [19]. Importantly, the specificity profile of this serine peptidase activity differs markedly from the chymotrypsin-like cercarial elastase that is secreted by the S. mansoni cercariae and from which we derive schistosomula [63, 70].…”

“…Schistosoma peptidases (a.k.a. proteases or proteolytic enzymes) are vital to successful parasitism, and facilitate invasion of the host, digestion of host proteins, reproduction, modulation of the host’s physiology [11–19] and immune response [14, 20]. Interference with these mechanisms by specific vaccines [21, 22] or drugs may provide therapeutic benefits.…”

Proteases and protease inhibitors in infectious diseases

“…Recently there has been a shift of attention to other serine proteases found in this organism and other helminths for the purpose of drug discovery. To this effect, several reviews and research articles have emerged …”

Comparative genomics of schistosomes: identifying parasites specific genes, drug and vaccine targets

“…After merging both surface and secretory proteins, 135 proteins (Supplementary Table 4.2) remained, of which 45 were predicted to be immunreactive (Supplementary [80][81][82][83][84][85][86] . These 20 proteins were further annotated using Swiss-Prot (Table 4.1).…”