A proteomic and functional study of the Schistosoma mansoni egg

• Main Author: Mathieson, William
• Published: University of York 2007
• Subjects: 591.9857
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485837

Newly released eggs of the parasitic wonn Schistosoma mansoni either pass through the gut wall to escape from the host or are washed away in the host's bloodstream. In the latter scenario most eggs become lodged in the host's liver, where they become the focus of a granulomatous response which can have severe pathological consequences. In this study, the S. mansoni soluble egg proteome is described and characterised for the first time. Mature eggs were separated from immature eggs and then fractionated into their morphological components: the miracidia, the hatch fluid (which bathes the miracidia) and the egg-secreted proteins. Each egg preparation was subjected to two-dimensional electrophoresis and tandem mass spectrometry. Developmental proteomic changes were then described in terms of the egg's morphology so insights into the egg's natural history were gained. For example, acquisition of aerobic respiratory enzymes by the miracidium was seen, but nevertheless the miracidium still favours the use of energy-efficient heat shock proteins. Western blotting was used to show that the immature egg adopts the ubiquitin-proteasome pathway to degrade its nutritive vitelline cells. The hatch fluid contains host proteins but it also has a defensive role, although its most abundant constituent (a large, acidic glycoprotein) is of unknown function. The egg-secreted proteins consist of different variants of just four proteins, one of which has a pro-protein convertase domain and another of which appears to be a general purpose binding protein. A protocol is devised to purify each variant, so further functional studies into the individual secreted proteins can be carried out in the future. The secreted proteins induce a profound proliferative response in lymphocytes from acutely infected mice, indicating that they may work by activating granuloma T cells to secrete pro-proteases that are subsequently activated, enabling the egg to cross the gut wall.