We characterized AA1 (Abscisic acid Activated 1), a protein from Lupinus luteus L. predicted to be located in the apoplastic space who’s mRNA and protein levels are strongly regulated by ABA, salt stress, and hypothermia. A fragment from the recombinant AA1 protein binds ABA as shown by the spectrofluorimetric titration assay of the protein by ABA. The BLAST software of the DFCI database identified more than 200 ESTs from 46 dicots and monocots, including three genes with unknown function from Arabidopsisthaliana, which are closely related to the lupine AA1. The central part of the proteins encoded by these genes contains the TolB motif from Escherichia coli and shares conserved WD40-like repeats, which form the basis for the tertiary beta-propeller structure and provide a potential platform for the assembly of protein complexes. Our data suggest that the highly conserved AA1 proteins from L. luteus and other higher plants are involved in ABA-mediated responses.