, 2007). Acute encephalitis develops check details in about 1–20 cases per 1000 infections, leading to death in 25% of cases and producing serious neurological lesions in 30% (Diagana et al., 2007; Jackson et al., 2007). Infections with Japanese encephalitis virus (JEV) are most often asymptomatic. Only one in 300 cases produce clinical features (Solomon, 1997). The first signs of infection

appear after an incubation period of between 6 and 14 days (Diagana et al., 2007). The disease usually begins with a high fever, chills, muscle pain and meningitis-type headaches accompanied by vomiting. The initial clinical features in children usually involve gastrointestinal symptoms (nausea, vomiting and abdominal pains). These nonspecific symptoms can continue for 2–4 days. After this period, the patient’s condition deteriorates RAD001 mouse rapidly. Eighty-five percent of subjects suffer from convulsions (Kumar et al., 1990). The meningeal syndrome predominates, causing painful neck stiffness. Additionally, motor paralyses including hemiplegia and tetraplegia may also occur. In about 30% of patients, tremor, rigidity, abnormal movements and other signs of extrapyramidal involvement

are present (Kumar et al., 1994). Recovery usually leaves serious behavioral and neurological sequelae such as persistently altered sensorium, extrapyramidal syndrome, epileptic seizures and severe mental retardation in children (Diagana et al., 2007). JE is a mosquito-borne arboviral infection caused by Flavivirus transmitted by anthropophilic rice field-breeding mosquitoes of the Culex species (mainly the Culex tritaeniorhynchus group). Vaccines have reduced the incidence of JE in some countries, but Non-specific serine/threonine protein kinase no specific antiviral therapy is currently available. Sampath & Padmanabhan (2009) pointed out the following molecular targets

for the flavivirus drug discovery: envelope glycoprotein, NS3 protease, NS3 helicase, NS5 methyltransferase and NS5 RNA-dependent RNA polymerase (Fig. 1). The NS3 protein (nonstructural protein 3) of JEV is a multifunctional protein combining protease, helicase, and nucleoside 5′-triphosphatase (NTPase) activities (Sampath & Padmanabhan, 2009). In particular, NS3 helicase/NTPase seems to be a promising antiviral drug target, as its enzymatic activity is essential for viral genome replication, transcription and translation (Yamashita et al., 2008). Recently, the crystal structure of the catalytic domain of JEV NS3 helicase/NTPase has been solved using a roentgenographic method with a resolution of 1.8 Å (Yamashita et al., 2008). JEV helicase, composed of three domains, displays an asymmetric distribution of charges on its surface, and contains a tunnel large enough to accommodate single-stranded RNA. Each of the motifs I (Walker A motif), II (Walker B motif) and VI contribute to the NTP-binding pocket. From mutation analysis (Yamashita et al.