An auxin-binding protein is localized to the plasma membrane of maize coleoptile cells: identification by photoaffinity labeling and purification of a 23-kda polypeptide.

Abstract

Plasma membrane vesicles were isolated from maize (Zea mays L.) coleoptile tissue by aqueous twophase partitioning and assayed for homogeneity by the use of membrane-specific enzymatic assays. Using 5-azido- [7-3H]indole-3-acetic acid ([3H]N3IAA), we identified several IAAbinding proteins with molecular masses of 60 kDa (pm6O), 58 kDa (pm58), and 23 kDa (pm23). Using Triton X-114, we were able to selectively extract pm23 from the plasma membrane. We show that auxins and functional analogues compete with[3H]N3IAA for binding to pm23. We found that PAB130, a polyclonal antibody raised against auxin-binding protein 1 (ABP-1), recognized ABP-1 as well as pm23. This suggests that pm23 shares common epitopes with ABP-1. In addition, we identified an auxin-binding protein with a molecular mass of 24 kDa (pm24), which was detected in microsomal but not in plasma membrane vesicle preparations. Like pm23 this protein was extracted from membrane vesicles with Triton X-1 14. We designed a purification scheme allowing simultaneous purification of pm23 and pm24. Homogeneous pm23 and pm24 were obtained from coleoptile extracts after 7000-fold purification.

A Soluble Auxin-Binding Protein from Hyoscyamus muticus Is a Glutathione S-Transferase

“…The photolabile, biologically active analog of IAA, azido-[3H]IAA, has been used for efficient screening for both membrane-bound and soluble ABPs (see Hicks et al, 1989;Jones and Venis, 1989;Macdonald et al, 1991;Feldwisch et al, 1992). Using this labeling reagent, we identified severa1 ABPs in the soluble fraction of Hyoscyamus muticus (Macdonald et al, 1991).…”

“…Severa1 such ABPs have been identified in the membrane and soluble fraction of different plant species (for reviews, see Jones, 1990, and refs. therein;Campos et al, 1992;Feldwisch et al, 1992;Palme et al, 1992), but whether one of these ABPs is an auxin receptor is still not clear.The search for the auxin receptor has mainly focused on membrane proteins. IAA, however, does nof necessarily need a receptor at the outer surface of the plasma membrane because the protonated (uncharged) form of this hydrophobic molecule penetrates the plasma membrane.…”

“…Severa1 such ABPs have been identified in the membrane and soluble fraction of different plant species (for reviews, see Jones, 1990, and refs. therein;Campos et al, 1992;Feldwisch et al, 1992;Palme et al, 1992), but whether one of these ABPs is an auxin receptor is still not clear.…”

5'-Azido-[3,6-3H2]-1-napthylphthalamic acid, a photoactivatable probe for naphthylphthalamic acid receptor proteins from higher plants: identification of a 23-kDa protein from maize coleoptile plasma membranes.

“…15). Further, an antibody raised against another maize auxin-binding protein, ABP-1 (40), which probably recognizes a highly conserved epitope within a variety of different auxin-binding proteins, also recognizes pm23 (41). This adds further credence to the significance of the photoaffinity labeling experiments presented here.…”

An Auxin Binding Protein is Localized in the Symbiosome Membrane of Soybean Nodules

“…Several auxin binding sites have been identified in the en-doplasmic reticulum, the tonoplast and the plas ma membrane [8] and proteins corresponding to these sites have been proposed to play a role in auxin perception or transport [9][10][11]. Using photoaffinity labeling with synthetic light-sensitive auxin analoges or auxin transport inhibitors, sev eral proteins were identified in mem brane frac tions of zucchini, tom ato and maize [11][12][13][14][15]. One o f the proteins that was identified by photoaffinity labeling in maize plasma mem branes was shown to be immunological related to another, now well studied, ER-located auxin binding protein [15].…”