title: Distinct N-terminal regulatory domains of Ca(2+)/H(+) antiporters.
abstract: The regulation of intracellular Ca(2+) levels is achieved in part by high-capacity vacuolar Ca(2+)/H(+) antiporters. An N-terminal regulatory region (NRR) on the Arabidopsis Ca(2+)/H(+) antiporter CAX1 (cation exchanger 1) has been shown previously to regulate Ca(2+) transport by a mechanism of N-terminal auto-inhibition. Here, we examine the regulation of other CAX transporters, both within Arabidopsis and from another plant, mung bean (Vigna radiata), to ascertain if this mechanism is commonly used among Ca(2+)/H(+) antiporters. Biochemical analysis of mung bean VCAX1 expressed in yeast (Saccharomyces cerevisiae) showed that N-terminal truncated VCAX1 had approximately 70% greater antiport activity compared with full-length VCAX1. A synthetic peptide corresponding to the NRR of CAX1, which can strongly inhibit Ca(2+) transport by CAX1, could not dramatically inhibit Ca(2+) transport by truncated VCAX1. The N terminus of Arabidopsis CAX3 was also shown to contain an NRR. Additions of either the CAX3 or VCAX1 regulatory regions to the N terminus of an N-terminal truncated CAX1 failed to inhibit CAX1 activity. When fused to N-terminal truncated CAX1, both the CAX3 and VCAX1 regulatory regions could only auto-inhibit CAX1 after mutagenesis of specific amino acids within this NRR region. These findings demonstrate that N-terminal regulation is present in other plant CAX transporters, and suggest distinct regulatory features among these transporters.
authors.affiliation: United States Department of Agriculture-Agricultural Research Service, Children's Nutrition Research Center, Baylor College of Medicine, 1100 Bates Street, Houston, TX 77030, USA.
authors.forename: Jon K
authors.initials: JK
authors.lastname: Pittman
authors.forename: Coimbatore S
authors.initials: CS
authors.lastname: Sreevidya
authors.forename: Toshiro
authors.initials: T
authors.lastname: Shigaki
authors.forename: Hanayo
authors.initials: H
authors.lastname: Ueoka-Nakanishi
authors.forename: Kendal D
authors.initials: KD
authors.lastname: Hirschi
mesh_terms: D000595:Amino Acid Sequence; D017920:Antiporters / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D003001:Cloning, Molecular; D007887:Fabaceae / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D006639:Histidine / Q000494:pharmacology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism*; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014617:Vacuoles / Q000378:metabolism
chemical_list: D017920:Antiporters; D002135:Calcium-Binding Proteins; D027682:Cation Transport Proteins; D010446:Peptide Fragments; C027614:calcium-hydrogen antiporters; D006639:Histidine; D009584:Nitrogen; D002118:Calcium