The sequences featured in this family are found repeated in a number of plant calmodulin-binding proteins (such as Q8W235 Q84ZT8 and Q8H6X1), and are thought to constitute the calmodulin-binding domains (PUBMED:12825696), (PUBMED:11684678). Binding of the proteins to calmodulin depends on the presence of calcium ions (PUBMED:12825696), (PUBMED:11684678). These proteins are thought to be involved in various processes, such as plant defence responses (PUBMED:12825696) and stolonisation or tuberization (PUBMED:11684678) .
This domain is found repeated in a number of plant calmodulin-binding proteins (such as Q8W235Q84ZT8 and Q8H6X1 ). It is thought to represent a calmodulin-binding domain [ (PUBMED:12825696) (PUBMED:11684678) ]. Binding of the proteins to calmodulin depends on the presence of calcium ions [ (PUBMED:12825696) (PUBMED:11684678) ]. Proteins containing this domain are thought to be involved in various processes, such as plant defence responses [ (PUBMED:12825696) ] and stolonisation or tuberization [ (PUBMED:11684678) ].
Characterization of a pathogen-induced calmodulin-binding protein: mappingof four Ca2+-dependent calmodulin-binding domains.
Plant Mol Biol. 2003; 52: 143-59
Display abstract
Ca2+ and calmodulin (CaM), a key Ca2+ sensor in all eukaryotes, have beenimplicated in defense responses in plants. To elucidate the role of Ca2+and CaM in defense signaling, we used 35S-labeled CaM to screen expressionlibraries prepared from tissues that were either treated with an elicitorderived from Phytophthora megasperma or infected with Pseudomonas syringaepv. tabaci. Nineteen cDNAs that encode the same protein, pathogen-inducedCaM-binding protein (PICBP), were isolated. The PICBP fusion proteinsbound 35S-CaM, horseradish peroxidase-labeled CaM and CaM-Sepharose in thepresence of Ca2+ whereas EGTA, a Ca2+ chelator, abolished binding,confirming that PICBP binds CaM in a Ca2+-dependent manner. Using a seriesof bacterially expressed truncated versions of PICBP, four CaM-bindingdomains, with a potential CaM-binding consensus sequence ofWSNLKKVILLKRFVKSL, were identified. The deduced PICBP protein sequence isrich in leucine residues and contains three classes of repeats. The PICBPgene is differentially expressed in tissues with the highest expression instem. The expression of PICBP in Arabidopsis was induced in response toavirulent Pseudomonas syringae pv. tomato carrying avrRpm1. Furthermore,PICBP is constitutively expressed in the Arabidopsis accelerated celldeath2-2 mutant. The expression of PICBP in bean leaves was also inducedafter inoculation with avirulent and non-pathogenic bacterial strains. Inaddition, the hrp1 mutant of Pseudomonas syringae pv. tabaci and inducersof plant defense such as salicylic acid, hydrogen peroxide and a fungalelicitor induced PICBP expression in bean. Our data suggest a role forPICBP in Ca2+-mediated defense signaling and cell-death. Furthermore,PICBP is the first identified CBP in eukaryotes with four Ca2+-dependentCaM-binding domains.
Isolation and characterization of a novel calmodulin-binding protein frompotato.
J Biol Chem. 2002; 277: 4206-14
Display abstract
Tuberization in potato is controlled by hormonal and environmentalsignals. Ca(2+), an important intracellular messenger, and calmodulin(CaM), one of the primary Ca(2+) sensors, have been implicated incontrolling diverse cellular processes in plants including tuberization.The regulation of cellular processes by CaM involves its interaction withother proteins. To understand the role of Ca(2+)/CaM in tuberization, wehave screened an expression library prepared from developing tubers withbiotinylated CaM. This screening resulted in isolation of a cDNA encodinga novel CaM-binding protein (potato calmodulin-binding protein (PCBP)).Ca(2+)-dependent binding of the cDNA-encoded protein to CaM is confirmedby (35)S-labeled CaM. The full-length cDNA is 5 kb long and encodes aprotein of 1309 amino acids. The deduced amino acid sequence showedsignificant similarity with a hypothetical protein from another plant,Arabidopsis. However, no homologs of PCBP are found in nonplant systems,suggesting that it is likely to be specific to plants. Using truncatedversions of the protein and a synthetic peptide in CaM binding assays wemapped the CaM-binding region to a 20-amino acid stretch (residues1216-1237). The bacterially expressed protein containing the CaM-bindingdomain interacted with three CaM isoforms (CaM2, CaM4, and CaM6). PCBP isencoded by a single gene and is expressed differentially in the tissuestested. The expression of CaM, PCBP, and another CaM-binding protein issimilar in different tissues and organs. The predicted protein containedseven putative nuclear localization signals and several strong PESTmotifs. Fusion of the N-terminal region of the protein containing six ofthe seven nuclear localization signals to the reporter genebeta-glucuronidase targeted the reporter gene to the nucleus, suggesting anuclear role for PCBP.
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