title: Mechanism of auxin interaction with Auxin Binding Protein (ABP1): a molecular dynamics simulation study.
abstract: Auxin Binding Protein 1 (ABP1) is ubiquitous in green plants. It binds the phytohormone auxin with high specificity and affinity, but its role in auxin-induced processes is unknown. To understand the proposed receptor function of ABP1 we carried out a detailed molecular modeling study. Molecular dynamics simulations showed that ABP1 can adopt two conformations differing primarily in the position of the C-terminus and that one of them is stabilized by auxin binding. This is in agreement with experimental evidence that auxin induces changes at the ABP1 C-terminus. Simulations of ligand egress from ABP1 revealed three main routes by which an auxin molecule can enter or leave the ABP1 binding site. Assuming the previously proposed orientation of ABP1 to plant cell membranes, one of the routes leads to the membrane and the other two to ABP1's aqueous surroundings. A network of hydrogen-bonded water molecules leading from the bulk water to the zinc-coordinated ligands in the ABP1 binding site was formed in all simulations. Water entrance into the zinc coordination sphere occurred simultaneously with auxin egress. These results suggest that the hydrogen-bonded water molecules may assist in protonation and deprotonation of auxin molecules and their egress from the ABP1 binding site.
authors.affiliation: Ruder Bosković Institute, Zagreb, Croatia.
authors.forename: Branimir
authors.initials: B
authors.lastname: Bertosa
authors.forename: Biserka
authors.initials: B
authors.lastname: Kojić-Prodić
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Wade
authors.forename: Sanja
authors.initials: S
authors.lastname: Tomić
mesh_terms: D001665:Binding Sites; D007210:Indoleacetic Acids / Q000737:chemistry*; D046912:Multiprotein Complexes / Q000737:chemistry / Q000648:ultrastructure; D010940:Plant Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D011485:Protein Binding; D011487:Protein Conformation; D025941:Protein Interaction Mapping / Q000379:methods*; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000648:ultrastructure*
chemical_list: D007210:Indoleacetic Acids; D046912:Multiprotein Complexes; D010940:Plant Proteins; D011956:Receptors, Cell Surface; C083846:auxin-binding protein 1