Neglected tropical diseases (NTDs) are responsible for most infections in poor countries [1] . Dengue is transmitted by Aedes (Stegomyia) aegypti (L.), and is one of the neglected diseases with the highest incidence in Brazil. This disease is caused by a RNA genome virus, and belonging to B group of arboviruses, genus flavivirus, family flaviviridae [1] . This virus has four immunologically distinct serotypes―DENV-1 to DENV-4. The first three are well known and documented in the Brazilian territory [2] -[4] , and DENV-4 serotype is discovered recently [5] .

Current strategies used to control mosquito and its larvae are based on techniques that integrate the reduction of reproduction sources and as addition of pitfalls [6] [7] . Other strategies include the use of Bacillus thuringiensis H-14 (Bti) (biopesticide), as well as the chemical insecticides from classes of pyrethroids, carbamates, organophosphates, diflubenzuron and triflumuron [8] [9] . Furthermore, the use of vaccines against Dengue virus has not reached any effective protection [10] [11] . With this restriction, the need to develop methodologies for mosquito control, using computational strategies, which can suggest new chemical compounds for testing in vivo against A. aegypti, is crucial for the reduction of Dengue incidence in underdeveloped countries [12] .

The arylalkylamine N-acetyltransferase (aaNAT) is a key enzyme that promotes acetyl-CoA transacetilation to arylalkylamines [13] [14] . In mammals, aaNAT is primarily involved in the synthesis of N-acetylserotonin and melatonin. This process is dependent on the N-acetylation of serotonin (5-hydroxytryptamine) and it is a limiting step of the process that regulates the circadian rhythm in mammals [15] [16] . In insects, the aaNATs play multiple roles: in addition to melatonin synthesis, aaNAT is involved in the inactivation of aromatic neurotransmitters and is essential in the cuticle sclerotization [17] . The aaNATs inactivate arylalkylamines such as octopamine, dopamine, and serotonin [18] [19] since insects have no monoamine oxidase (MAO) [20] [21] .

The cuticular exoskeleton gives the insect a rigid layer and prevents direct contact with the external environment, avoiding infections and injury. This structure is important for the mechanical support and flexibility. During its lifetime, the mosquito periodically exchanges the old cuticle and produces a new one [22] . In developing this new cuticle, insects undergo a process called sclerotization, where it is hard and darkened. Because it is important for vector survival, the use of a key enzyme in cuticle formation is a good way to block A. aegypti development [22] [23] . There are two sclerotization precursors: N-acetyldopamine and N-β-alanyldopamine. The first one is an aaNAT product and shows that this enzyme holds a special place in the insect cuticle sclerotization [24] [25] .

Molecular Docking studies allow us to analyze the orientation of the molecule (ligand/inhibitor), describing the affinity of a given molecule to a protein-binding site [26] . Virtual screening of chemicals is one of the main techniques currently used in Drug Discovery, testing natural and synthesized compounds [27] [28] . Online databases and cheminformatics tools, such as ZINC [29] and SEA [30] , respectively, allow comparison between previous used compounds and millions of deposited structures.

The aim of this study is to perform a virtual screening for new potential inhibitors, selected from online databases that can form complexes with aaNAT from A. aegypti, using molecular docking approach.

The crystal structure of aaNAT was obtained from Protein Data Bank (www.pdb.org) [31] , with the code 1L0C. We used PyMOL 1.7.4.4 [32] to check the protein about possible structure crashes and the positions of amino acids from active site. Then the protein was used for docking studies.

After ligand searching and comparison in ZINC, PubChem, and SAM databases, we selected three compounds (Figure 1), which could interact with aaNAT. Docking poses, affinity energies, as well as Hydrogen bond acceptor (HbA) and Hydrogen bond donor (HbD) information about each molecule in the complex are shown in Table 1. Coa-S-acetyltryptamine (CoASAT) is the molecule that reaches best affinity energy and HbA/HbD characteristics, followed by 3-indoleacriloil-coenzyme, and 3-coenzyme-A indolepropionil with lowest energy.

The biochemical activity of aaNAT is closely associated to inactivation of neurotransmitters. This possibility is supported by the fact that (1) capacity of acetylating various neurotransmitters/arylalkylamines; (2) the N-aceti- ldopamine was found in the head of the mosquito fed dopamine; (3) these genes are expressed in the mosquito’s head [39] . An accumulation of neurotransmitters like dopamine in the synaptic cleft can cause various damages, since Aedes aegypti have no monoamine oxidase A and B (MAOA and MAOB), the most important inactivators of neurotransmitters [39] and this prolonged signaling may be fatal.

Blocking aaNAT, the cuticle formation process is impaired, and it will affect the development of the adult mosquito, since this is essential for joint motion, mechanical support, and protects it from external environment, and rust infections. There is also the excessive burning of neurotransmitters in the synaptic cleft, since they use aaNAT to inactivate neurotransmitters. Two studies with Bombyx mori (silkworm) showed that loss of aaNAT function results in the formation of a cuticle with strong dark staining [39] , confirming that there is an intimate involvement of aaNAT with cuticle formation.

The representation of the ligands interacting with the active site of aaNAT is shown in Figure 2. It is noted that all ligands interact in the same active site than the crystallographic inhibitor (CoASAT) [40] .

The Aedes aegypti is still a target of numerous health campaigns in Brazil, in order to reduce Dengue contamination. The use of Cheminformatics and Structural Biology is strongly valid to propose new chemical structures that interact with some key metabolism enzymes of this mosquito.

This study used the aaNAT, a catalytic enzyme with great importance in the lifecycle of A. aegypti. Using a known inhibitor and accessing online molecules databases, it was possible to reach some analogues that could be used as new inhibitors.

Results showed that CoASAT (−8.9 kcal/mol) and IACoA (−8.9 kcal/mol) have a better interaction with the target, considering energy affinity and number of interactions with the amino acids from aaNAT active site, while 3-indolepropionyl coenzyme A showed the smallest affinity energy as well as number of interactions in the active site. In addition, we suggest these compounds to be tested in vivo against larvae and adult A. aegypti.

We would like to thank FAPESB for providing undergraduate student scholarships and financial help to this study.

The authors declare that they have no competing interests.

BL: Virtual Screening, Docking and write the manuscript; MS: Virtual Screening; EO: Generated interaction maps; WS: Write manuscript; AGN: Write manuscript, revise English; GS: Write manuscript; BA: Virtual Screening, Docking, generated interaction maps, write the manuscript and supervised the study.

Bruno LuisAlves Lourenço,Maicon ViníciusAraújo Santos Silva,Elisson Barrosde Oliveira,Wagner Rodriguesde Assis Soares,AristótelesGóes-Neto,GesivaldoSantos,Bruno SilvaAndrade, (2015) Virtual Screening and Molecular Docking for Arylalkylamine-N-Acetyltransferase (aaNAT) Inhibitors, a Key Enzyme of Aedes (Stegomyia) aegypti (L.) Metabolism. Computational Molecular Bioscience,05,35-44. doi: 10.4236/cmb.2015.53005