Fetuin-A, a Hepatocyte-Specific Protein That BindsPlasmodium bergheiThrombospondin-Related Adhesive Protein: a Potential Role in Infectivity

Abstract

Malaria infection is initiated when the insect vector injectsPlasmodium sporozoites into a susceptible vertebrate host. Sporozoites rapidly leave the circulatory system to invade hepatocytes, where further development generates the parasite form that invades and multiplies within erythrocytes. Previous experiments have shown that the thrombospondin-related adhesive protein (TRAP) plays an important role in sporozoite infectivity for hepatocytes. TRAP, a typical type-1 transmembrane protein, has a long extracellular region, which contains two adhesive domains, an A-domain and a thrombospondin repeat. We have generated recombinant proteins of the TRAP adhesive domains. These TRAP fragments show direct interaction with hepatocytes and inhibit sporozoite invasion in vitro. When the recombinant TRAP A-domain was used for immunoprecipitation against hepatocyte membrane fractions, it bound to ␣2-Heremans-Schmid glycoprotein/ fetuin-A, a hepatocyte-specific protein associated with the extracellular matrix. When the soluble sporozoite protein fraction was immunoprecipitated on a fetuin-A-adsorbed protein A column, TRAP bound this ligand. Importantly, anti-fetuin-A antibodies inhibited invasion of hepatocytes by sporozoites. Further, onset of malaria infection was delayed in fetuin-A-deficient mice compared to that in wild-type C57BL/6 mice when they were challenged with Plasmodium berghei sporozoites. These data demonstrate that the extracellular region of TRAP interacts with fetuin-A on hepatocyte membranes and that this interaction enhances the parasite's ability to invade hepatocytes.Malaria is a deadly parasitic disease which affects nearly 40% of the world's population. In any given year 300 to 500 million clinical cases occur, with more than a million deaths. Malaria is caused by species of the protozoan parasite Plasmodium. The infection is initiated when a female Anopheles mosquito injects Plasmodium sporozoites into a susceptible vertebrate host. The sporozoites migrate to the liver, where they undergo many rounds of schizogony in the hepatocytes. The resulting merozoites then invade and multiply within erythrocytes, causing the clinical symptoms of malaria.Understanding the pathogenesis of malaria requires a keen understanding of the molecular mechanisms used by Plasmodium to recognize and invade host cells. Invasion is mediated by interactions between specific parasite molecules and complementary ligands on the host cells. Plasmodium has three invasive stages: (i) sporozoites (sporogonic cycle), which invade the salivary glands of the mosquito; (ii) salivary gland sporozoites (exoerythrocytic cycle), which invade hepatocytes in the vertebrate; and (iii) merozoites (erythrocytic cycle), which invade erythrocytes. The invasion of hepatocytes by sporozoites has been known to require two parasite proteins: circumsporozoite protein (CS) and thrombospondin-related adhesive protein (TRAP) (6,28,30,33,34,44). These proteins are conserved in all Plasmodium species examined to date (26,40) and are present on the parasit...

Reprogramming the specificity of sortase enzymes

“…4 C and D), identified by mass spectrometry and confirmed by Western blot as fetuin A. As a systematic regulator of tissue mineralization (21), the selective in vivo and in vitro modification of endogenous fetuin A may be useful in the study of pathogenic biomineralization, as well as the diagnosis or potential treatment of fetuin-associated hemodialysis (22) and Plasmodium berghei pathogenesis (23). Fetuin A contains an LPPAG sequence that our studies above suggest should be a substrate for eSrtA(4S-9), but should not be an effective substrate for eSrtA.…”

“…Although fetuin A is traditionally difficult to purify away from its natively interacting partners (34), our strategy of site-specific reaction and pull-down afforded pure preparations of truncated fetuin A without detectable contaminants. Additionally, the modification of fetuin A raises a number of new research and therapeutic opportunities, including the in situ stabilization of the protein to potentially effect mortality outcomes in hemodialysis (22), the study of its proposed roles in hepatocyte invasion by P. berghei (23), and its role in insulin sensitivity (35).…”

Shape change in the receptor for gliding motility in Plasmodium sporozoites

“…In invasion, a moving junction containing TRAP is formed between the parasite and hepatocyte plasma membranes as the parasitophorous vacuole is formed around the sporozoite (6,24,25). Thus far, understanding of the ligands encountered by the sporozoite on its long journey is meager, but the list includes heparin (24,(26)(27)(28). Our ability to produce well-folded TRAP and characterize a putative high affinity state promises to further advance ligand identification.…”

Fetuin-A Regulation of Calcified Matrix Metabolism

“…Plasmodium sporozoites use fetuin-A binding to "hitch-hike" their way into liver cells, 27 suggesting that fetuin-A function is indispensable and despite negative selection pressure has been maintained long enough for this docking mechanism to evolve. Soon after its discovery, fetuin has been shown to inhibit trypsin.…”