Caleosin of Arabidopsis thaliana: Effect of Calcium on Functional and Structural Properties

A non-radioactive blot binding assay has proved the capacity of a purified recombinant form of Arabidopsis thaliana caleosin (AtCio1), a key protein of this plant oil body, to bind calcium. Calcium affected recombinant caleosin aggregation state, solubility, and electrophoretic mobility on SDS-PAGE. The effect of calcium on interfacial behavior of recombinant caleosin was studied at three interfaces: air/water (A/W), purified oil/water (OM), and air/phosholipid/water (A/PLs/W). Recombinant caleosin was able to decrease interfacial tension (IFT) at A/W and O/W interfaces as a function of concentration and calcium, whereas no interaction was detected at the A/PLs/W interface. Effect of calcium was time dependent, and its amplitude strongly varied with the interface considered. Reconstituted oil bodies were used to prove the involvement of recombinant caleosin in their calcium-driven aggregation and coalescence. Calcium ions at concentration as low as 100 nM were able to strongly modify the shape and aggregation state of purified oil bodies, as well as their behavior within a monolayer, reflecting potentially profound changes in their structure and dynamic.