Calmodulin-like (CML) proteins are major EF-hand-containing, calcium (Ca2+)-binding proteins with crucial roles in plant development and in coordinating plant stress tolerance. Given their abundance in plants, the properties of Ca2+ sensors and identification of novel target proteins of CMLs deserve special attention. To this end, we recombinantly produced and biochemically characterized CML36 from Arabidopsis thaliana. We analyzed Ca2+ and Mg2+ binding to the individual EF-hands, observed metal-induced conformational changes, and identified a physiologically relevant target. CML36 possesses two high-affinity Ca2+/Mg2+ mixed binding sites and two low-affinity Ca2+-specific sites. Binding of Ca2+ induced an increase in the alpha-helical content and a conformational change that lead to the exposure of hydrophobic regions responsible for target protein recognition. Cation binding, either Ca2+ or Mg2+, stabilized the secondary and tertiary structures of CML36, guiding a large structural transition from a molten globule apo-state to a compact holoconformation. Importantly, through in vitro binding and activity assays, we showed that CML36 interacts directly with the regulative N terminus of the Arabidopsis plasma membrane Ca2+-ATPase isoform 8 (ACA8) and that this interaction stimulates ACA8 activity. Gene expression analysis revealed that CML36 and ACA8 are co-expressed mainly in inflorescences. Collectively, our results support a role for CML36 as a Ca2+ sensor that binds to and modulates ACA8, uncovering a possible involvement of the CML protein family in the modulation of plant-autoinhibited Ca2+ pumps.

Arabidopsis Calmodulin-like Protein CML36 is a Calcium (Ca2+) Sensor that Interacts with the Plasma Membrane Ca2+-ATPase Isoform ACA8 and Stimulates its Activity / A. Astegno, M.C. Bonza, R. Vallone, V. La Verde, M. D’Onofrio, L. Luoni, B. Molesin, P. Dominici. - In: JOURNAL OF BIOLOGICAL CHEMISTRY. - ISSN 1083-351X. - 292:36(2017), pp. 15049-15061. [10.1074/jbc.M117.787796]

Arabidopsis Calmodulin-like Protein CML36 is a Calcium (Ca2+) Sensor that Interacts with the Plasma Membrane Ca2+-ATPase Isoform ACA8 and Stimulates its Activity

M.C. Bonza
Secondo
;
L. Luoni;
2017

Abstract

Calmodulin-like (CML) proteins are major EF-hand-containing, calcium (Ca2+)-binding proteins with crucial roles in plant development and in coordinating plant stress tolerance. Given their abundance in plants, the properties of Ca2+ sensors and identification of novel target proteins of CMLs deserve special attention. To this end, we recombinantly produced and biochemically characterized CML36 from Arabidopsis thaliana. We analyzed Ca2+ and Mg2+ binding to the individual EF-hands, observed metal-induced conformational changes, and identified a physiologically relevant target. CML36 possesses two high-affinity Ca2+/Mg2+ mixed binding sites and two low-affinity Ca2+-specific sites. Binding of Ca2+ induced an increase in the alpha-helical content and a conformational change that lead to the exposure of hydrophobic regions responsible for target protein recognition. Cation binding, either Ca2+ or Mg2+, stabilized the secondary and tertiary structures of CML36, guiding a large structural transition from a molten globule apo-state to a compact holoconformation. Importantly, through in vitro binding and activity assays, we showed that CML36 interacts directly with the regulative N terminus of the Arabidopsis plasma membrane Ca2+-ATPase isoform 8 (ACA8) and that this interaction stimulates ACA8 activity. Gene expression analysis revealed that CML36 and ACA8 are co-expressed mainly in inflorescences. Collectively, our results support a role for CML36 as a Ca2+ sensor that binds to and modulates ACA8, uncovering a possible involvement of the CML protein family in the modulation of plant-autoinhibited Ca2+ pumps.
Plant glutamate-decarboxylase; ion-binding-properties; N-terminus; saccharomyces-cervisiae; reference genes; thaliana; expression; mechanism; NMR; magnesium
Settore BIO/04 - Fisiologia Vegetale
Settore BIO/10 - Biochimica
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/518600
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