Proteomic analysis of adult Ascaris suum fluid compartments and secretory products

Abstract

Background: Strategies employed by parasites to establish infections are poorly understood. The host-parasite interface is maintained through a molecular dialog that, among other roles, protects parasites from host immune responses. Parasite excretory/secretory products (ESP) play major roles in this process. Understanding the biology of protein secretion by parasites and their associated functional processes will enhance our understanding of the roles of ESP in host-parasite interactions.

Methodology/principal findings: ESP was collected after culturing 10 adult female Ascaris suum. Perienteric fluid (PE) and uterine fluid (UF) were collected directly from adult females by dissection. Using SDS-PAGE coupled with LC-MS/MS, we identified 175, 308 and 274 proteins in ESP, PE and UF, respectively. Although many proteins were shared among the samples, the protein composition of ESP was distinct from PE and UF, whereas PE and UF were highly similar. The distribution of gene ontology (GO) terms for proteins in ESP, PE and UF supports this claim. Comparison of ESP composition in A. suum, Brugia malayi and Heligmosoides polygyrus showed that proteins found in UF were also secreted by males and by larval stages of other species, suggesting that multiple routes of secretion may be used for homologous proteins. ESP composition of nematodes is both phylogeny- and niche-dependent.

Conclusions/significance: Analysis of the protein composition of A. suum ESP and UF leads to the conclusion that the excretory-secretory apparatus and uterus are separate routes for protein release. Proteins detected in ESP have distinct patterns of biological functions compared to those in UF. PE is likely to serve as the source of the majority of proteins in UF. This analysis expands our knowledge of the biology of protein secretion from nematodes and will inform new studies on the function of secreted proteins in the orchestration of host-parasite interactions.

Figure 1. Distribution of proteins among ESP, PE and UF.

The Venn diagram shows the numbers of proteins shared between and among the three compartments based on common Accession Number.

Figure 2. Distribution of level 2 molecular functions GO terms for proteins from UF, PE, ESP and ESP-UF.

The three fractions are represented by different colors. ESP-UF refers to the proteins found in ESP but not in UF.

Figure 3. Distribution of level 4 molecular functions GO terms for proteins from UF, PE, ESP and ESP-UF.

The three fractions are represented by different colors. ESP-UF refers to the proteins found in ESP but not in UF.

Figure 4. Distribution of level 2 biological processes GO terms for proteins from UF, PE, ESP and ESP-UF.

The three fractions are represented by different colors. ESP-UF refers to the proteins found in ESP but not in UF.

Figure 5. Distribution of level 4 biological processes GO terms for proteins from UF, PE, ESP and ESP-UF.

The three fractions are represented by different colors. ESP-UF refers to the proteins found in ESP but not in UF.

Figure 6. Percentage of protein similarity among UF, UF-ESP, ESP and ESP-UF from female A. suum and ESP from adult B. malayi.

Percent similarity among UF, UF-ESP, ESP and ESP-UF from female A. suum and female, male and total adult B. malayi ESP. The comparison is based on annotation names for proteins in the various compartments, confirmed by BlastP analysis.

Figure 7. Cross-species comparisons of secreted proteins.

Depicted is percent similarity of proteins in UF, UF-ESP, ESP and ESP-UF from A. suum with ESP from B. malayi and H. polygyrus. Comparisons are based on annotation names for proteins in the various samples, confirmed by BlastP analysis.