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Characterization of the Brassica rapa auxin amido-hydrolase, BrILL2

Reversible conjugation with amino acids is used by plants to adjust endogenous auxin levels as required for concerted growth and development. One of the auxin-amidohydrolases included in this regulatory mechanism, BrILL2, was cloned from Chinese cabbage (Brassica rapa L.) and tested for hydrolytic activity towards conjugates of indole-3-acetic acid. We further characterized the enzyme including substrates such as alanine (Ala) conjugates of indole-3-propionic acid (IPA) and indole-3-butyric acid (IBA), both of which are endogenous auxins. Enzymatic activity of purified BrILL2 was tested in the presence of dithiothreitol and Mn++. Progress of the cleavage reaction was monitored by HPLC using absorbance at 284 nm. IPA-ala was hydrolyzed at the highest rate, followed by IBA-ala and IAA-ala, in this order. The 3D structure of Br-ILL2 was modeled by the program Modeller9v2 using the X-ray structure of IAA-aminoacid hydrolase from Arabidopsis thaliana (PDB_id 1XMB) and the Mn++ binding site was determined. Ligands: IBA-Ala, IPA-ala, IAA-Ala and IPA-Asp were docked into the protein using the AutoDock3.05 program. The most populated binding site was selected as the most probable one. The obtain complexes were neutralized by adding Na+ ions, the systems was solvated in the 8 Å ; ; thick water layer and energy minimized using the program AMBER9. To learn more about the complex stability and the substrate binding site we accomplished a series of molecular dynamics simulations.

Auxin amido-hydrolase; BrILL2; Brassica rapa; Amino acid conjugates; Enzymatic activity

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