Interaction of auxin-binding protein 1 with maize coleoptile plasma membranes in vitro

In a search for membrane "docking proteins" interacting with Zea mays auxin-binding protein (ABP1) the binding of purified ABP1 to maize coleoptile plasma-membrane vesicles was investigated. Concentration-dependent, saturable binding of ABP1 to the membrane vesicles was observed in binding assays using 10(-8)-10(-6) M ABP1. Biotinylated ABP1 was displaced from the membrane binding sites by competition with unlabeled ABP1, demonstrating specific binding. The association step proved to be pH-dependent with maximum binding at pH 5.0 or lower. Auxins did not influence the ABP1 binding to plasma-membrane vesicles, but ABP1 associated with plasma-membrane vesicles was still able to specifically bind [3H]naphthalene-1-acetic acid. The rather stable interaction of ABP1 with plasma-membrane vesicles was only affected by strong alkaline buffers or detergents. The binding capacity was calculated to be in the range of 0.2 pmol ABP1 per g coleoptile fresh weight.