Purification and Characterization of a Barley Aleurone Abscisic Acid-binding Protein

Abstract

A protein designated ABAP1 and encoded by a novel gene (GenBank TM accession number AF127388) was purified and shown to specifically bind abscisic acid (ABA). ABAP1 protein is a 472-amino acid polypeptide containing a WW protein interaction domain and is induced by ABA in barley aleurone layers. Polyclonal antiidiotypic antibodies (AB2) cross-reacted with purified ABAP1 and with a corresponding 52-kDa protein associated with membrane fractions of ABA-treated barley aleurones. ABAP1 genes were detected in diverse monocot and dicot species, including wheat, tobacco, alfalfa, garden pea, and oilseed rape. Our data show that ABAP1 exerts high binding affinity for ABA. The interaction is reversible, follows saturation kinetics, and has stereospecificity, thus meeting the criteria for an ABA-binding protein.

Abscisic acid is an endogenous cytokine in human granulocytes with cyclic ADP-ribose as second messenger

“…8B) ABA-binding sites in intact human granulocytes. The K d of the high-affinity binding site was 11 nM, similar to that described for ABA-binding proteins in plants (16)(17)(18)(19), and the number of ABA-binding sites per cell (B max ϭ 6,000) was similar to that reported for G protein linked chemokine receptors in granulocytes (20). The K d of the low-affinity binding site (K d ϭ 500 M) was several logs higher than that of the high-affinity binding site, indicating that these binding sites are most likely not involved in ABA binding and signaling at the concentrations used in this study (50 nM to 20 M).…”

“…Taken together, these results indicate that ABA-binding sites occur on the surface of human granulocytes, although influx of ABA into granulocytes and interaction with intracellular receptor(s) cannot be ruled out. In plants, both intracellular and cell surface ABA-binding sites have been described (16)(17)(18)(19), but neither receptor type has been as yet molecularly identified, with the exception of an RNA-binding nuclear protein recently demonstrated to bind ABA in vitro (21). In plants, a significant proportion of intracellular ABA is conjugated to glucosyl groups (22): the very high number of low-affinity ABA binding sites per cell in granulocytes (B max ϭ 6 ϫ 10 7 ) suggests the possibility that they represent similar intracellular storage forms of ABA and/or of ABA catabolites.…”

Conservation and Divergence of FCA Function between Arabidopsis and Rice

“…This clone appears to consist of more than simply a truncated version of the OsFCA clone, as it harbors a 3¢ UTR which is longer than that of OsFCA, and is also longer than that of the AK073225 clone. Razem et al (2004) isolated an ABA-binding protein, ABAP1, from the aleurone layer of barley, which we determined to be a sequence homologue of the AK05849 clone. Therefore, we are unable to dismiss the possibility that the AK05849 clone encodes for a functional protein.…”

Transient expression of AtNCED3 and AAO3 genes in guard cells causes stomatal closure in Vicia faba

“…In contrast, there have been several studies suggesting an intracellular reception site in guard cells (Schwartz et al 1994;Hamilton et al 2000;Levchenko et al 2005). A number of studies to isolate ABA receptor(s) have been conducted, and several proteins have been isolated as having ABA binding activity (Zhang et al 2002;Razem et al 2004). Recently, two intracellular receptor candidates, RNA-binding protein FCA (Razem et al 2006) and Mgchelatase H subunit (CHLH) (Shen et al 2006), have been isolated.…”