title: Cloning and characterization of CXIP1, a novel PICOT domain-containing Arabidopsis protein that associates with CAX1.
abstract: Regulation of Ca(2+) transporters is a vital component of signaling. The Arabidopsis H(+)/Ca(2+) exchanger CAX1 contains an N-terminal autoinhibitory domain that prevents Ca(2+) transport when CAX1 is heterologously expressed in yeast. Using a yeast screen, we have identified three different proteins that activate CAX1. One of these, CXIP1 (CAX-interacting protein-1; 19.3 kDa) has amino acid similarity to the C terminus of PICOT (protein kinase C-interacting cousin of thioredoxin) proteins. Although PICOT proteins are found in a variety of organisms, a function has not been previously ascribed to a plant PICOT protein. We demonstrate that CXIP1 activated the CAX1 homolog CAX4, but not CAX2 or CAX3. An Arabidopsis homolog of CXIP1 (CXIP2) weakly activated CAX4, but not CAX1. In a yeast two-hybrid assay, CXIP1 interacted with the N terminus of CAX1. In competition analysis, CXIP1 and a CAX1 N-terminal peptide appeared to bind to similar N-terminal domains of CAX1. Chimeric CAX3 constructs containing the N terminus of CAX1 were activated by CXIP1. In Arabidopsis, CXIP1 transcripts, like CAX1, accumulated in response to different metal conditions. This work thus characterizes a new class of signaling molecules in plants that may regulate CAX transporters in vivo.
authors.affiliation: United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Ning-Hui
authors.initials: NH
authors.lastname: Cheng
authors.forename: Kendal D
authors.initials: KD
authors.lastname: Hirschi
mesh_terms: D000595:Amino Acid Sequence; D017920:Antiporters / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D003001:Cloning, Molecular; D017124:Conserved Sequence; D007700:Kinetics; D008969:Molecular Sequence Data; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D017920:Antiporters; D029681:Arabidopsis Proteins; C473126:CXIP1 protein, Arabidopsis; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D027682:Cation Transport Proteins; C027614:calcium-hydrogen antiporters