Monoamine Neurotransmitters as Substrates for Novel Tick Sulfotransferases, Homology Modeling, Molecular Docking, and Enzyme Kinetics

Authors

Emine Bihter Yalcin, University of Rhode Island
Hubert Strangl, University of Rhode Island
Sivakamasundari Pichu, University of Rhode Island
Thomas N. Mather, University of Rhode IslandFollow
Roberta S. King, University of Rhode IslandFollow

Document Type

Article

Date of Original Version

2011

Department

Biomedical and Pharmaceutical Sciences

Abstract

Blacklegged ticks (Ixodes scapularis) transmit the causative agent of Lyme disease in the Northeastern United States. Current research focuses on elucidating biochemical pathways that may be disrupted to prevent pathogen transmission, thereby preventing disease. Genome screening reported transcripts coding for two putative sulfotransferases in whole tick extracts of the nymphal and larval stages. Sulfotransferases are known to sulfonate phenolic and alcoholic receptor agonists such as 17β-estradiol, thereby inactivating the receptor ligands. We used bioinformatic approaches to predict substrates for Ixosc Sult 1 and Ixosc Sult 2 and tested the predictions with biochemical assays. Homology models of 3D protein structure were prepared, and visualization of the electrostatic surface of the ligand binding cavities showed regions of negative electrostatic charge. Molecular docking identified potential substrates including dopamine, R-octopamine and S-octopamine, which docked into Ixosc Sult 1 with favorable binding affinity and correct conformation for sulfonation. Dopamine, but not R- or S-octopamine, also docked into Ixosc Sult 2 in catalytic binding mode. The predictions were confirmed using cytosolic fractions of whole tick extracts. Dopamine was a good substrate (K_m = 0.1−0.4 μM) for the native Ixodes scapularis sulfotransferases from larval and nymphal stages regardless of their fed/unfed status. Octopamine sulfonation was detected only after feeding when gene expression data suggests that Ixosc Sult 1 is present. Because dopamine is known to stimulate salivation in ticks through receptor stimulation, these results imply that the function(s) of Ixosc Sult 1 or 2 may include inactivation of the salivation signal via sulfonation of dopamine and/or octopamine.

Citation/Publisher Attribution

Yalcin, E. B., Strangl, H., Pichu, S., Mather, T. N., & King, R. S. (2011). Monoamine Neurotransmitters as Substrates for Novel Tick Sulfotransferases, Homology Modeling, Molecular Docking, and Enzyme Kinetics. ACS Chem. Biol., 6(2), 176-178. doi: 10.1021/cb100266g

Available at: https://doi.org/10.1021/cb100266g

Comment

Emine Bihter Yalcin, Hubert Strangl and Roberta S. King are from the Department of Biomedical and Pharmaceutical Sciences.

Sivakamasundari Pichu and Thomas N. Mather are from the Department of Plant Sciences and Entomology.