Antiviral activity of flavonoids present in aerial parts of Marcetia taxifolia against Hepatitis B virus, Poliovirus, and Herpes Simplex Virus in vitro.

Marcetia taxifolia is a neotropical plant present in South America and it has been evaluated in several biological models due to the presence of active metabolites. Nevertheless, there is a limited quantity of studies related to the antiviral activity of the compounds present in this genus. In our work, the antiviral effect of the compounds isolated from the aerial parts of Marcetia taxifolia was evaluated against Hepatitis B virus (HBV), Herpes Simplex Virus type 1 (HSV-1), and Poliovirus type 1 (PV-1). The cytopathic effect and viral quantification by qPCR were determined as indicative of antiviral activity. Our data show that myricetin rhamnoside (MyrG), myricetin-3-α-O-ramnosil (1→6)-α-galactoside (MyrGG), 5,3'-dihydroxy-3,6,7,8,4'-pentamethoxyflavone (PMF), 5-hydroxy-3,6,7,3',4'pentamethoxyflavone (PMF-OH) had antiviral activity without cytotoxic effects. The methoxyflavones PMF and PMF-OH were the most active compounds, showing an antiviral effect against all the evaluated viruses. Computational studies showed that these compounds could interact with the Reverse Transcriptase. Altogether, these results suggest that the flavonoids (related to myricetin and methoxyflavones) are the main antiviral compounds present in the aerial parts of Marcetia taxifolia. Furthermore, our results showed that the methoxyflavones have a broad antiviral activity, which represents an opportunity to evaluate these flavonoids as lead molecules to develop new antiviral compounds.

Comparative analyses of the ß-tubulin gene and molecular modeling reveal molecular insight into the colchicine resistance in kinetoplastids organisms.

Differential susceptibility to microtubule agents has been demonstrated between mammalian cells and kinetoplastid organisms such as Leishmania spp. and Trypanosoma spp. The aims of this study were to identify and characterize the architecture of the putative colchicine binding site of Leishmania spp. and investigate the molecular basis of colchicine resistance. We cloned and sequenced the ß-tubulin gene of Leishmania (Viannia) guyanensis and established the theoretical 3D model of the protein, using the crystallographic structure of the bovine protein as template. We identified mutations on the Leishmania ß-tubulin gene sequences on regions related to the putative colchicine-binding pocket, which generate amino acid substitutions and changes in the topology of this region, blocking the access of colchicine. The same mutations were found in the ß-tubulin sequence of kinetoplastid organisms such as Trypanosoma cruzi, T. brucei, and T. evansi. Using molecular modelling approaches, we demonstrated that conformational changes include an elongation and torsion of an α-helix structure and displacement to the inside of the pocket of one ß-sheet that hinders access of colchicine. We propose that kinetoplastid organisms show resistance to colchicine due to amino acids substitutions that generate structural changes in the putative colchicine-binding domain, which prevent colchicine access.

The 6-phosphogluconate dehydrogenase of Leishmania (Leishmania) mexicana: gene characterization and protein structure prediction.

6-Phosphogluconate dehydrogenase (6PGDH) is a key enzyme of the oxidative branch involved in the generation of NADPH and ribulose 5-phosphate. In the present work, we describe the cloning, sequencing and characterization of a 6PGDH gene from Leishmania (Leishmania) mexicana. The gene encodes a polypeptide chain of 479 amino acid residues with a predicted molecular mass of 52 kDa and a pI of 5.77. The recombinant protein possesses a dimeric quaternary structure and displays kinetic parameter values intermediate between those reported for Trypanosoma brucei and T. cruzi with apparent K(m) values of 6.93 and 5.2 µM for 6PG and NADP(+), respectively. The three-dimensional structure of the enzymes of Leishmania and T. cruzi were modelled from their amino acid sequence using the crystal structure of the enzyme of T. brucei as template. The amino acid residues located in the 6PGDH C-terminal region, which are known to participate in the salt bridges maintaining the protein dimeric structure, differed significantly among the enzymes of Leishmania, T. cruzi, and T. brucei. Our results strongly suggest that 6PGDH can be selected as a potential target for the development of new therapeutic drugs in order to improve existing chemotherapeutic treatments against these parasites.

Structure of C-terminal fragment of merozoite surface protein-1 from Plasmodium vivax determined by homology modeling and molecular dynamics refinement.

One current vaccine candidate against Plasmodium vivax targeting asexual blood stage is the major merozoite surface protein-1 of P. vivax (PvMSP-1). Vaccine trials with PvMSP-1(19) and PvMSP-1(33) have succeeded in protecting monkeys and a large proportion of individuals, naturally exposed to P. vivax transmission, develop specific antibodies to PvMSP-1(19). This study presents a model for the three-dimensional structure of the C-terminal 19kDa fragment of P. vivax MSP-1 determined by means of homology modeling and molecular dynamics refinement. The structure proved to be consistent with MSP-1(19) of known crystal or solution structures. The presence of a main binding pocket, well suited for protein-protein interactions, was determined by CASTp. Corrections reported to the sequence of PvMSP-1(19) Belem strain were also inspected. Our model is currently used as a basis to understand antibody interactions with PvMSP-1(19).