Fragment Molecular Orbital Study of the Interaction between Sarco/Endoplasmic Reticulum Ca²⁺-ATPase and its Inhibitor Thapsigargin toward Anti-Malarial Development

Plasmodium falciparum, the causative agent of malignant malaria, is insensitive to thapsigargin (TG), a well-known inhibitor of the human sarco/endoplasmic reticulum Ca2+-ATPase (SERCA). To understand the key factor causing the difference of the sensitivity, the molecular interaction of TG and each SERCA was analyzed by the fragment molecular orbital (FMO) method. While the major component of the interaction energy was the nonpolar interaction, the major difference in the molecular interaction arose from the polar interaction, namely, the hydrogen bonding interaction with a hydroxyl group of TG. Additionally, we successfully confirmed these FMO calculation results by measuring the inhibitory activity of a synthesized TG derivative. Our calculations and experiments indicated that, by replacing the hydroxyl group of TG with another functional group, the sensitivities of TG to human and P. falciparum SERCAs can be reversed. This study provides important information to develop antimalarial compounds targeting P. falciparum SERCA

List of primers used in this study.

List of primers used in this study.</p

Pathogens identified in different districts in Sistan and Baluchestan province.

Pathogens identified in different districts in Sistan and Baluchestan province.</p

Total Synthesis of (±)-Lundurine B

A total synthesis of (±)-lundurine B was accomplished. A combination of stereoselective intramolecular cyclopropane formation and aryl amination furnished cyclopropane-fused indoline stereoselectively. Ring-closing metathesis (RCM) of siloxy diene and intramolecular aminoacetal formation followed by bridgehead vinylation of an anti-Bredt iminium cation led to the construction of six- and seven-membered rings with a quaternary carbon center. After the formation of dihydropyrrole by RCM, the Boc-protecting group of indoline was converted into the corresponding methyl carbamate via silyl carbamate to complete the total synthesis of (±)-lundurine B. The characteristic rearrangement of the cyclopropane-fused indoline skeleton is also described

Co-infection of pathogens in goat samples from Sistan and Baluchestan province.

Co-infection of pathogens in goat samples from Sistan and Baluchestan province.</p

Factors associating with the infection evaluated by Fisher’s exact test.

Factors associating with the infection evaluated by Fisher’s exact test.</p

Multivariate logistic regression analysis of the factors associating with the infection.

Multivariate logistic regression analysis of the factors associating with the infection.</p

Three phase processes of the red blood cell (RBC) invasion by <i>Plasmodium yoelii</i>.

<p>Time-lapse imaging of RBC invasion was captured every 0.1 sec with transmitted light for <i>P. yoelii</i> 17XL (A), <i>P. yoelii</i> 17X1.1 (B), and <i>Plasmodium falciparum</i> 3D7 line (C). First “Pre-invasion” phase started from the initial attachment between the merozoite (0 second, arrow head) and RBC plasma membrane, followed by the RBC deformation, and apical reorientation of the merozoite (rightmost column of “Pre-invasion” phase). Second “Invasion” phase consisted of the internalization of a merozoite into RBC and a rapid rotary movement of the internalized merozoite (arrow). Final “Echinocytosis” phase was defined as RBC being deformed to spike-like shape. The bars represent 5 µm.</p

Fisher’s exact test for the coinfection of two pathogens.

Fisher’s exact test for the coinfection of two pathogens.</p

Kinetic difference in red blood cell (RBC) invasion between <i>Plasmodium</i> species.

<p>The median time for each step are shown as a box plot with whiskers from minimum to maximum. The interquartile range shows as box with the median marked as a horizontal line, minimum and maximum from lower and upper quartile represent error bar. <i>P</i> values were determined using the Mann-Whitney U test. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050780#pone.0050780.s001" target="_blank">Table S1</a> for detail values.</p