PLANT PHYSIOLOGY , Vol 102, Issue 1 29-34, Copyright © 1993 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
A Soluble Auxin-Binding Protein from Hyoscyamus muticus Is a Glutathione S-Transferase
J. Bilang, H. Macdonald, P. J. King and A. Sturm
Friedrich Miescher-Institut, P.O.Box 2543, CH-4002 Basel, Switzerland
We have used the photoaffinity label azido-[3H]IAA (5-N3-
[7-3H]indole-3-acetic acid), a biologically active analog of
indole-3-acetic acid, to identify auxin-binding proteins (ABPs) in the
soluble fraction of Hyoscyamus muticus. A 25-kD polypeptide previously
described (H. Macdonald, A.M. Jones, P.J. King [1991] J Biol Chem 266:
7393-7399) has now been purified to homogeneity by conventional methods.
Binding of azido-[3H]IAA to the purified protein was reduced by active
auxins but not by inactive indoles. Partial amino acid sequences of the
purified protein showed high homology to glutathione S-transferase (GST)
from tobacco (ParB) and from maize (GT32). The conclusion that the 25-kD
ABP is a GST is further supported by high GST activity in fractions highly
enriched in the 25-kD polypeptide and recognition of the ABP by antibodies
against GST from wheat and maize. Furthermore, purification of a protein
from a soluble protein extract from H. muticus by affinity chromatography
on glutathione-agarose also yielded a 25-kD polypeptide that was
indistinguishable in its N-terminal amino acid sequence and biochemical
characteristics from the protein purified by conventional methods. Possible
functions of GST in auxin action are discussed.
