Identification of a novel stress regulated FERM domain containing cytosolic protein having PTP activity in Setaria cervi, a bovine filarial parasite

Identification of glucose regulated protein94 (GRP94) in filarial parasite S. cervi and its expression under ER stress

GRP94, a member of HSP90 family, is involved in folding and degradation of endoplasmic reticulum proteins. The proteome analysis of Setaria cervi, a bovine filarial parasite showed that a 91 kDa protein was over expressed, after the parasites were maintained in glucose deprived medium. The MALDI- LC/MS analysis of the 91 kDa band confirmed it as endoplasmin precursor (GRP94). Amino acid sequence alignment of S.cervi GRP94 exhibited maximum similarity with human filarial parasite Wuchereria bancrofti, Brugia malayi and Loa loa GRP94. Tunicamycin treatment of S. cervi worms revealed that the expression of GRP94 is associated with ER stress. Transcription of S. cervi grp94 as well as igf is regulated by transcription factors ATF-6 and XBP-1S which was confirmed by Real Time PCR. Moreover, marked alteration in the expression of igf after 3 h and 6 h of drug treatment suggested propagation of survival pathway under ER stress. The activities of ER stress markers protein disulphide isomerase and glycosyltransferase were significantly reduced after 6 h of tunicamycin treatment. The present findings thus indicate that the expression of GRP94 and regulation of its expression is under ER stress in Setaria cervi. To our knowledge this is the first report of identification of GRP94, in any filarial parasite till date.

Molecular cloning, purification and characterization of Brugia malayi phosphoglycerate kinase

Phosphoglycerate kinase (PGK) is a glycolytic enzyme present in many parasites. It has been reported as a candidate molecule for drug and vaccine developments. In the present study, a full-length cDNA encoding the Brugia malayi 3-phosphoglycerate kinase (BmPGK) with an open reading frame of 1.3 kb was isolated and PCR amplified and cloned. The exact size of the BmPGK's ORF is 1377 bps. The BmPGK gene was subcloned into pET-28a (+) expression vector, the expressed enzyme was purified by affinity column and characterized. The SDS-PAGE analysis revealed native molecular weight of recombinant Brugia malayi 3-phosphoglycerate kinase (rBmPGK) to be ∼45 kDa. The enzyme was found sensitive to temperature and pH, it showed maximum activity at 25 °C and pH 8.5. The K_m values for PGA and ATP were 1.77 and 0.967 mM, respectively. The PGK inhibitor, clorsulon and antifilarial drugs albendazole and ivermectin inhibited the enzyme. The specific inhibitor of PGK, clorsulon, competitively inhibited enzyme with K_i value 1.88 μM. Albendazole also inhibited PGK competitively with K_i value 35.39 μM. Further these inhibitory studies were confirmed by docking and molecular simulation of drugs with enzyme. Clorsulon interacted with substrate binding site with glutamine 37 as well as in hinge regions with aspartic acid 385 and valine 387 at ADP binding site. On the other hand albendazole interacted with asparagine 335 residues. These effects were in good association with binding interactions. Thus current study might help in designing and synthesis of effective inhibitors for this novel drug target and understanding their mode of interaction with the potent anthelmintic drugs.

Inhibition of Setaria cervi protein tyrosine phosphatases by Phenylarsine oxide: A proteomic and biochemical study

Phenylarsine oxide (PAO), a specific protein tyrosine phosphatase (PTP) inhibitor significantly decreased the motility and viability of Setaria cervi ultimately leading to its death. The PTP activity present in the cytosolic and detergent soluble fractions as well as on surface of these parasites was significantly inhibited by PAO. A marked alteration in protein spots abundance after proteomic analysis showed 14 down-regulated and 9 upregulated spots in the treated parasites as compared to the control. The PTP inhibition led to increase in the cytosolic and mitochondrial calpain activity in these parasites. PAO also blocked the ATP generation in the parasite depicted by reduced activity of phosphoglycerate kinase and expression of enolase. An increased ROS level, induced lipid peroxidation/protein carbonyl formation and decreased activity of different antioxidant enzymes like thioredoxin reductase, glutathione reductase and glutathione transferases was also observed in the PAO treated parasites. PAO, thus disturbs the overall homeostasis of the filarial parasite by inhibiting PTPs. Thereby suggesting that these molecules could be used as a good chemotherapeutic target for lymphatic filariasis.

Identification and characterization of novel membrane-bound PRL protein tyrosine phosphatases from Setaria cervi, a bovine filarial parasite

A significant amount of protein tyrosine phosphatase (PTP) activity was detected in the detergent-soluble membrane-bound fraction of Setaria cervi, a bovine filarial parasite. The membrane-bound PTP activity was significantly inhibited when the adult parasites were exposed to compounds having antifilarial activity like aspirin and SK7 as well as phenylarsine oxide, a specific PTP inhibitor suggesting that this activity is stress regulated. Further, this enzyme was purified as a single protein of apparently 21 kDa using two different chromatographic techniques. The MALDI-MS/MS analysis of its peptides showed closest match with protein tyrosine phosphatase PRL (Aedes aegypti). This purified enzyme (named as PRL) showed maximum activity at pH 5.5/37 °C and hydrolysed para nitro phenyl phosphate (pNPP) at the highest rate followed by O-P-L-tyrosine and O-P-L-threonine. It showed significant inhibition by specific inhibitors of PTP such as sodium orthovanadate, phenylarsine oxide and ammonium molybdate and was activated by dithiothreitol (DTT). The active site modification studies suggested involvement of cysteine, arginine, histidine and aspartic acid in the catalytic activity of PRL. The activity of S. cervi PRL was also found to be resistant towards the external oxidative stress. Thus, S. cervi PRL could be taken as a potential target for the management of human lymphatic filariasis.