Delineation of the Structural Elements of Oriental Liver Fluke PLA2 Isoforms for Potent Drug Designing

Abstract

Clonorchis sinensis or the Chinese liver fluke is one of the most prevalent parasites affecting a major population in the oriental countries. The parasite lacks lipid generating mechanisms but is exposed to fatty acid rich bile in the liver. A secretory phospholipase A 2 , an enzyme that breaks down complex lipids, is important for the growth of the parasite. The enzyme is also implicated in the pathogenesis leading up to the hepatic fibrosis and its complications including cancer. The five isoforms of this particular enzyme from the parasite therefore qualify as potential drug targets. In this study, a detailed structural and ligand binding analysis of the isoforms has been done by modeling. The overall three dimensional structures of the isoforms are well conserved with three helices and a bwing stabilized by four disulfide bonds. There are characteristic differences at the calcium binding loop, hydrophobic channel and the C-terminal domain that can potentially be exploited for drug binding. But the most significant feature pertains to the catalytic site where the isoforms exhibit three variations of either a histidineaspartate-tyrosine or histidine-glutamate-tyrosine or histidine-aspartate-phenylalanine. Molecular docking studies show that isoform specific residues and their conformations in the substrate binding hydrophobic channel make unique interactions with certain inhibitor molecules resulting in a perfect tight fit. The proposed ligand molecules have a predicted affinity in micro-molar to nano-molar range. Interestingly, few of the ligand binding interaction patterns is in accordance to the phylogenetic studies to thereby establish the usefulness of evolutionary mechanisms in aiding ligand design. The molecular diversity of the parasitic PLA 2 described in this study provides a platform for personalized medicine in the therapeutics of clonorchiasis.

Secreted phospholipase A2 of Clonorchis sinensis activates hepatic stellate cells through a pathway involving JNK signalling

“…The histidine conformation is critical for PLA2 to hydrolyse the phospholipids [13]. The protein itself is an enzyme, and therefore, there are two ways for it to work.…”

“…The sn-2 ester bond of phospholipids is hydrolysed by phospholipase A2 enzyme through a nucleophile water molecule and catalytic histidine. The histidine conformation is critical for PLA2 to hydrolyse the phospholipids [ 13 ]. The protein itself is an enzyme, and therefore, there are two ways for it to work.…”

“…The parasite lives in the bile duct of the liver and is exposed to bile which is rich in fatty acid . Cs sPLA2, which was proved to be a component of the ESPs of C. sinensis , plays an important role in the growth of the parasite by breaking down complex lipids [ 12 , 13 ]. Liver fibrosis is observed in patients with moderate or severe infection of liver fluke.…”

<p>Human Secretary Phospholipase A2 Mutations and Their Clinical Implications</p>

“…19 This difference at the active site between the target enzyme and the housekeeping human isoform is, therefore, an important structural parameter that can be exploited to designspecific drug molecules against the parasite Clonorchis sinensis. 20 Unlike several sPLA 2 s in reptiles and scorpions that exist in solution as stable multichain complexes in the form of homodimers, homotrimers and heterodimers, native human sPLA 2 s do not have quaternary conformations. 21,22 The human GIII sPLA 2 has a C-terminal extension that is reminiscent of the nonenzymatic subunit of a sPLA 2 from a scorpion that is associated with main enzymatic subunit by a disulfide bond.…”

<p>Structural Modeling of Wild and Mutant Forms of Human Plasma Platelet Activating Factor-Acetyl Hydrolase Enzyme</p>

“…20,21 In accordance, the mutations such as V279F and Q281R on pPAF-AH too have been known to have critical and favorable cardiovascular outcomes. [22][23][24][25] Structural characterization of the PLA 2 group of enzymes has helped: (1) to understand the structure-function relationship of PLA 2 enzymes; 26 (2) to sub-classify the groups and sub-groups within the PLA 2 family; 27 (3) to understand the mechanism of PLA 2 induced toxicity; 28 (4) to delineate the structural elements of druggable PLA 2 s for potent drug design; 28,29 (6) to pave the way for personalised medicine in PLA 2 mediated diseases; 30 (7) to understand the effect of mutations on PLA 2 enzyme function and thereby their impact on clinical phenotypes. 31 In this study, we have carried out modeling studies of wild and mutant forms of pPAF-AH to understand the implications of mutations V279F, Q281R, V279F +Q281R on their respective structures.…”