Soap, a novel malaria ookinete protein involved in mosquito midgut invasion and oocyst development

Johannes T. Dessens, Inga Sidén-Kiamos, Jacqui Mendoza, Vassiliki Mahairaki, Emad Khater, Dina Vlachou, Xiao Jin Xu, Fotis C. Kafatos, Christos Louis, George Dimopoulos, Robert E. Sinden

Research output: Contribution to journalArticlepeer-review

96 Scopus citations


An essential, but poorly understood part of malaria transmission by mosquitoes is the development of the ookinetes into the sporozoite-producing oocysts on the mosquito midgut wall. For successful oocyst formation newly formed ookinetes in the midgut lumen must enter, traverse, and exit the midgut epithelium to reach the midgut basal lamina, processes collectively known as midgut invasion. After invasion ookinete-to-oocyst transition must occur, a process believed to require ookinete interactions with basal lamina components. Here, we report on a novel extra-cellular malaria protein expressed in ookinetes and young oocysts, named secreted ookinete adhesive protein (SOAP). The SOAP gene is highly conserved amongst Plasmodium species and appears to be unique to this genus. It encodes a predicted secreted and soluble protein with a modular structure composed of two unique cysteine-rich domains. Using the rodent malaria parasite Plasmodium berghei we show that SOAP is targeted to the micronemes and forms high molecular mass complexes via disulphide bonds. Moreover, SOAP interacts strongly with mosquito laminin in yeast-two-hybrid assays. Targeted disruption of the SOAP gene gives rise to ookinetes that are markedly impaired in their ability to invade the mosquito midgut and form oocysts. These results identify SOAP as a key molecule for ookinete-to-oocyst differentiation in mosquitoes.

Original languageEnglish (US)
Pages (from-to)319-329
Number of pages11
JournalMolecular Microbiology
Issue number2
StatePublished - Jul 2003
Externally publishedYes

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology


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