Abstract
Ca(2+) levels in plants, fungi, and bacteria are controlled in part by H(+)/Ca(2+) exchangers; however, the relationship between primary sequence and biological activity of these transporters has not been reported. The Arabidopsis H(+)/cation exchangers, CAX1 and CAX2, were identified by their ability to suppress yeast mutants defective in vacuolar Ca(2+) transport. CAX1 has a much higher capacity for Ca(2+) transport than CAX2. An Arabidopsis thaliana homolog of CAX1, CAX3, is 77% identical (93% similar) and, when expressed in yeast, localized to the vacuole but did not suppress yeast mutants defective in vacuolar Ca(2+) transport. Chimeric constructs and site-directed mutagenesis showed that CAX3 could suppress yeast vacuolar Ca(2+) transport mutants if a nine-amino acid region of CAX1 was inserted into CAX3 (CAX3-9). Biochemical analysis in yeast showed CAX3-9 had 36% of the H(+)/Ca(2+) exchange activity as compared with CAX1; however, CAX3-9 and CAX1 appear to differ in their transport of other ions. Exchanging the nine-amino acid region of CAX1 into CAX2 doubled yeast vacuolar Ca(2+) transport but did not appear to alter the transport of other ions. This nine-amino acid region is highly variable among the plant CAX-like transporters. These findings suggest that this region is involved in CAX-mediated Ca(2+) specificity.
Abstract from the paper’s OpenAlex record; open copy licensed cc-by. Read at the source ↗
The text the model read, with the source record’s inline markup (italics, sub- and superscripts) rendered and its character entities decoded; quote offsets refer to the raw text.
Claims 10
Claim · model-written summary
CAX1 had higher Ca(2+) transport capacity than CAX2.
Not reportedTaxon
Verbatim
e0“CAX1 has a much higher capacity for Ca(2+) transport than CAX2”
Claim · model-written summary
CAX3 is 77% identical to CAX1.
- Taxon
- Arabidopsis thaliana
Arabidopsis thalianae0 - Gene
- CAX3e0
- Outcome
- identicale0
- Value
- 77%e0
- Comparator
- CAX1e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“An Arabidopsis thaliana homolog of CAX1, CAX3, is 77% identical (93% similar)”
Claim · model-written summary
CAX3 localized to the yeast vacuole but did not suppress the transport-defective mutants.
- Outcome
- localized to the vacuole but did not suppress yeast mutants defective in vacuolar Ca(2+) transporte0
Not reportedTaxon
Verbatim
e0“when expressed in yeast, localized to the vacuole but did not suppress yeast mutants defective in vacuolar Ca(2+) transport”
Claim · model-written summary
Insertion of a nine-amino acid CAX1 region enabled CAX3 to suppress yeast transport mutants.
- Treatment
- a nine-amino acid region of CAX1 was inserted into CAX3e0
- Gene
- CAX3e0
- Outcome
- suppress yeast vacuolar Ca(2+) transport mutantse0
Not reportedTaxonComparatorDirection
Verbatim
e0“CAX3 could suppress yeast vacuolar Ca(2+) transport mutants if a nine-amino acid region of CAX1 was inserted into CAX3 (CAX3-9)”
Claim · model-written summary
CAX3-9 had 36% of CAX1 H(+)/Ca(2+) exchange activity.
Not reportedTaxon
Verbatim
e0“CAX3-9 had 36% of the H(+)/Ca(2+) exchange activity as compared with CAX1”
Claim · model-written summary
CAX3-9 and CAX1 differed in transport of other ions.
Not reportedTaxon
Verbatim
e0“CAX3-9 and CAX1 appear to differ in their transport of other ions”
Claim · model-written summary
Putting the CAX1 region into CAX2 doubled yeast vacuolar calcium transport.
- Treatment
- Exchanging the nine-amino acid region of CAX1 into CAX2e0
- Gene
- CAX2e0
- Outcome
- yeast vacuolar Ca(2+) transporte0
- Direction
- doublede0
Not reportedTaxonComparator
Verbatim
e0“Exchanging the nine-amino acid region of CAX1 into CAX2 doubled yeast vacuolar Ca(2+) transport”
Claim · model-written summary
That CAX1 region did not appear to alter CAX2 transport of other ions.
Not reportedTaxonTreatmentComparator
Verbatim
e0“but did not appear to alter the transport of other ions”
Claim · model-written summary
The nine-amino acid region was highly variable among plant CAX-like transporters.
Verbatim
e0“This nine-amino acid region is highly variable among the plant CAX-like transporters”
Claim · model-written summary
The authors infer that this region participates in CAX-mediated calcium specificity.
Not reportedTaxon
Verbatim
e0“These findings suggest that this region is involved in CAX-mediated Ca(2+) specificity”