Molecular characterization of the major hemelipoglycoprotein in ixodid ticks

The major hemelipoglyco-carrier protein (CP) found throughout the development of male and female adult American dog ticks, Dermacentor variabilis (Say) was sequenced. DvCP is a single transcript coding for two protein subunits that together contain three motifs: (1) a lipoprotein n-terminal domain that is a common attribute of proteins that bind lipids, carbohydrates and metals; (2) a domain of unknown function characteristic of proteins with several large open beta sheets; and (3) a von Willebrand factor type D domain near the carboxy-terminus apparently important for multimerization. These motifs, which are also found in tick vitellogenin, are not shared by heme-binding proteins studied thus far in other hematophagous insects. DvCP message was highest in fat body and salivary gland but was also found in midgut and ovary tissue. Expression was initiated by blood feeding in virgin females and not by mating, as is typical of tick vitellogenin; and the message was found in fed males at levels similar to part fed, virgin females. CP appears to be highly conserved among the Ixodida. The closest match by BlastP to DvCP is vitellogenin from Caenorhabditis elegans (AAC04423), suggesting that CP is a novel protein. The role of CP in heme sequestration, the evolution of hematophagy and host complementation are discussed.