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Calmodulin/Ca 2+ ‐ATPase interaction at the Arabidopsis thaliana plasma membrane is dependent on calmodulin isoform showing isoform‐specific Ca 2+ dependencies
Author(s) -
Luoni Laura,
Bonza Maria Cristina,
De Michelis Maria Ida
Publication year - 2006
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.2006.00588.x
Subject(s) - calmodulin , gene isoform , dissociation constant , atpase , biochemistry , arabidopsis thaliana , chemistry , enzyme , binding site , c terminus , microbiology and biotechnology , biology , receptor , mutant , amino acid , gene
Arabidopsis thaliana plasma membrane (PM) Ca 2+ ‐ATPase is a type IIB P‐type ATPase, which binds calmodulin (CaM) to an autoinhibitory N‐terminal domain. Here, we took advantage of the fact that PM isolated from cultured cells mainly contains At ‐ACA8, the first cloned A. thaliana PM Ca 2+ ‐ATPase, to analyse its interaction with CaM in detail. Analysis of the ability of different peptides designed from At ‐ACA8 N‐terminus to compete with the native protein for binding of bovine brain CaM (bbCaM) showed that peptide 41 I‐T 63 had the same affinity of the native protein [apparent dissociation constant (KD) at 10 µ M free Ca 2+ about 25 n M ], thus localizing At ‐ACA8 CaM‐binding site within this sequence. The interaction of At ‐ACA8 N‐terminus with bbCaM, as determined by surface plasmon resonance, was rapid, and slowly but was fully reversible. Analysis of Ca 2+ ‐ATPase activation as a function of the concentration of different isoforms of A. thaliana CaM showed that Ca 2+ ‐ATPase is activated to similar extent by bbCaM and by different isoforms of homologous CaM. However, the affinity for the divergent A. thaliana isoform CaM8 was lower than that for canonical CaM isoforms such as A. thaliana CaM2, CaM4 and CaM6 or bbCaM. The apparent KD for CaM isoforms of the native enzyme increased with the decrease of free Ca 2+ concentration, suggesting that enzyme conformation is affected by Ca 2+ . Binding of CaM isoforms to At ‐ACA8 N‐terminus was affected differently by free Ca 2+ concentration, suggesting that plant CaMs may have different affinities for Ca 2+ .