High-resolution crystal structure of FKBP12 from Aedes aegypti

The Potential of Biologically Active Brazilian Plant Species as a Strategy to Search for Molecular Models for Mosquito Control

Natural products are a valuable source of biologically active compounds and continue to play an important role in modern drug discovery due to their great structural diversity and unique biological properties. Brazilian biodiversity is one of the most extensive in the world and could be an effective source of new chemical entities for drug discovery. Mosquitoes are vectors for the transmission of dengue, Zika, chikungunya, yellow fever, and many other diseases of public health importance. These diseases have a major impact on tropical and subtropical countries, and their incidence has increased dramatically in recent decades, reaching billions of people at risk worldwide. The prevention of these diseases is mainly through vector control, which is becoming more difficult because of the emergence of resistant mosquito populations to the chemical insecticides. Strategies to provide efficient and safe vector control are needed, and secondary metabolites from plant species from the Brazilian biodiversity, especially Cerrado, that are biologically active for mosquito control are herein highlighted. Also, this is a literature revision of targets as insights to promote advances in the task of developing active compounds for vector control. In view of the expansion and occurrence of arboviruses diseases worldwide, scientific reviews on bioactive natural products are important to provide molecular models for vector control and contribute with effective measures to reduce their incidence.

Larvicidal Compounds Extracted from Helicteres velutina K. Schum (Sterculiaceae) Evaluated against Aedes aegypti L

Helicteres velutina K. Schum (Sterculiaceae), a member of Malvaceae sensu lato, is a Brazilian endemic plant that has been used by the indigenous tribe Pankarare as an insect repellent. A previous study has reported the isolation of terpenoids, flavonoids and pheophytins, in addition to the larvicidal activity of crude H. velutina extracts derived from the aerial components (leaves, branches/twigs, and flowers). The present study reports the biomonitoring of the effects of fractions and isolated compounds derived from H. velutina against A. aegypti fourth instar larvae. A crude ethanol extract was submitted to liquid–liquid extraction with hexane, dichloromethane, ethyl acetate and n-butanol to obtain their respective fractions. Larvicidal evaluations of the fractions were performed, and the hexane and dichloromethane fractions exhibited greater activities than the other fractions, with LC₅₀ (50% lethal concentration) values of 3.88 and 5.80 mg/mL, respectively. The phytochemical study of these fractions resulted in the isolation and identification of 17 compounds. The molecules were subjected to a virtual screening protocol, and five molecules presented potential larvicidal activity after analyses of their applicability domains. When molecular docking was analysed, only three of these compounds showed an ability to bind with sterol carrier protein-2 (1PZ4), a protein found in the larval intestine. The compounds tiliroside and 7,4′-di-O-methyl-8-O-sulphate flavone showed in vitro larvicidal activity, with LC₅₀ values of 0.275 mg/mL after 72 h and 0.182 mg/mL after 24 h of exposure, respectively. This is the first study to demonstrate the larvicidal activity of sulphated flavonoids against A. aegypti. Our results showed that the presence of the OSO₃H group attached to C-8 of the flavonoid was crucial to the larvicidal activity. This research supports the traditional use of H. velutina as an alternative insecticide for the control of A. aegypti, which is a vector for severe arboviruses, such as dengue and chikungunya.

C-H…O hydrogen bonds in FK506-binding protein-ligand interactions

Hydrogen bonds are important interaction forces observed in protein structures. They can be classified as stronger or weaker depending on their energy, thereby reflecting on the type of donor. The contribution of weak hydrogen bonds is deemed as an important factor toward structure stability along with the stronger bonds. One such bond, the C-H…O type hydrogen bond, is shown to make a contribution in maintaining three dimensional structures of proteins. Apart from their presence within protein structures, the role of these bonds in protein-ligand interactions is also noteworthy. In this study, we present a statistical analysis on the presence of C-H…O hydrogen bonds observed between FKBPs and their cognate ligands. The FK506-binding proteins (FKBPs) carry peptidyl cis-trans isomerase activity apart from the immunosuppressive property by binding to the immunosuppressive drugs FK506 or rapamycin. Because the active site of FKBPs is lined up by many hydrophobic residues, we speculated that the prevalence of C-H…O hydrogen bonds will be considerable. In a total of 25 structures analyzed, a higher frequency of C-H…O hydrogen bonds is observed in comparison with the stronger hydrogen bonds. These C-H…O hydrogen bonds are dominated by a highly conserved donor, the C(α/β) of Val55 and an acceptor, the backbone oxygen of Glu54. Both these residues are positioned in the β4-α1 loop, whereas the other residues Tyr26, Phe36 and Phe99 with higher frequencies are lined up at the opposite face of the active site. These preferences could be implicated in FKBP pharmacophore models toward enhancing the ligand affinity. This study could be a prelude to studying other proteins with hydrophobic pockets to gain better insights into ligand recognition.

Classical force field parameters for two high-affinity ligands of FKBP12

FKBP12 is an important target in the treatment of transplant rejection and is also a promising target for cancer and neurodegenerative diseases. We determined for two ligands of nanomolar affinity the set of parameters in the CHARMM force field. The fitting procedure was based on reproducing the quantum chemistry data (distances, angles, and energies). Since the dynamical behavior of such ligands strongly depends on the dihedral angles, care was taken to derive the corresponding parameters. Moreover, since each of the central core region of these two ligands is similar to other known ligands or drugs of other proteins, part at least of these parameters could also be useful for these other ligands.

Solution structure of FK506-binding protein 12 from Aedes aegypti

Dengue remains one of the major public concerns as the virus eludes the immune response. Currently, no vaccines or antiviral therapeutics are available for dengue prevention or treatment. Immunosuppressive drug FK506 shows an antimalarial activity, and its molecular target, FK506-binding protein (FKBP), was identified in human Plasmodium parasites. Likewise, a conserved FKBP family protein has also been identified in Aedes aegypti (AaFKBP12), which is expected to play a similar role in the life cycle of Aedes aegypti, the primary vector of dengue virus infection. As FKBPs belong to a highly conserved class of immunophilin family and are involved in key biological regulations, they are considered as attractive pharmacological targets. In this study, we have determined the nuclear magnetic resonance solution structure of AaFKBP12, a novel FKBP member from Aedes aegypti, and presented its structural features, which may facilitate the design of potential inhibitory ligands against the dengue-transmitting mosquitoes.