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Title: Aedes aegypti juvenile hormone acid methyl transferase, the ultimate enzyme in the biosynthetic pathway of juvenile hormone III, exhibits substrate control

Author
item VAN EKERT, EVELIEN - University Of Florida
item HEYLEN, KEVIN - Leuven University
item ROUGE, PIERRE - University Hospital Center Of Toulouse
item POWELL, CHARLES - University Of Florida
item Shatters, Robert - Bob
item SMAGGHE, GUY - Ghent University
item BOROVSKY, DOV - Dov Borovsky

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2014
Publication Date: 3/20/2014
Citation: Van Ekert, E., Heylen, K., Rouge, P., Powell, C.A., Shatters, R.G., Smagghe, G., Borovsky, D. 2014. Aedes aegypti juvenile hormone acid methyl transferase, the ultimate enzyme in the biosynthetic pathway of juvenile hormone III, exhibits substrate control. Journal of Insect Physiology. 64:62-73.

Interpretive Summary: In the search for environmentally safe alternative to pest insect control through heavy reliance on chemical pesticides, research was conducted on a specific molecule insects use to control developmental processes: insect juvenile hormone. The hope is to develop new insect control strategies based on the specific interdiction of this control point. In this report, research was performed to identify genes and their associated proteins that are involved in the synthesis of insect juvenile hormone. This is the first report showing the enzyme involved in the final steps of mosquito juvenile hormone synthesis. The enzymes identified in controlling this process are now presented as excellent targets for the development of new mosquito control strategies, and by extrapolation to other insects, opens the door for targeting this process for the control of numerous insect pests in agriculture.

Technical Abstract: We report on the cloning, sequencing, characterization, 3D modeling and docking of Aedes aegypti juvenile hormone acid methyl transferase (AeaJHAMT), the enzyme that converts juvenile hormone acid (JHA) into juvenile hormone (JH). Purified recombinant AeaJHAMT was extensively characterized for enzymatic activity and the Michaelis Menten kinetic parameters Km, Vmax, kcat¬ (turn over number) and kcat/Km (catalytic efficiency) using JHA and its analogues as substrates. AeaJHAMT methylates JHA III 5-fold faster than farnesoic acid (FA). Significant differences in lower methyl transferase (MT) activities towards the cis/trans/trans, cis/trans/cis and the trans/cis/cis isomers of JHA I (1.32, 4.71 and 156-fold, respectively) indicate that substrate chirality is important for proper alignment at the catalytic cavity and for efficient methyl transfer by S-adenosyl methionine (SAM). Our 3D model shows a potential binding site below the main catalytic cavity for JHA analogues causing conformational change and steric hindrance in the transfer of the methyl group to JHA III. These, in silico, observations were corroborated by, in vitro, studies showing that several JHA analogues are potent inhibitors of AeaJHAMT. In vitro, and in vivo studies using [3H-methyl]SAM show that the enzyme is present and active throughout the adult life stage of A. aegypti. Tissue specific expressions of the JHAMT gene of A. aegypti (jmtA) transcript during the life cycle of A. aegypti show that AeaJHAMT is a constitutive enzyme and jmtA transcript is expressed in the corpora allata (CA), and the ovary before and after the blood meal. These results indicate that JH III can be synthesized from JHA III by the mosquito ovary, suggesting that ovarian JH III may play an important physiological role in ovarian development and reproduction. Incubating AeaJHAMT with highly pure synthetic substrates indicates that JHA III is the enzyme's preferred substrate, suggesting that AeaJHAMT is the ultimate enzyme in the biosynthetic pathway of JH III.