Plasma membrane calcium ATPase activity is regulated by actin oligomers through direct interaction.

DALGHI MG1, FERNÁNDEZ MM, FERREIRA-GOMES M, MANGIALAVORI IC, MALCHIODI EL, STREHLER EE, ROSSI JP.

JOURNAL OF BIOLOGICAL CHEMISTRY

AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC

Lugar: Bethesda, Maryland; Año: 2013 vol. 288 p. 23380 - 23393

0021-9258

SUMMARY As recently described by our group, Plasma Membrane Calcium ATPase (PMCA) activity can be regulated by the actin cytoskeleton. In this study, we characterize the interaction of purified G-actin with isolated PMCA and examine the effect of G-actin during the first polymerization steps. As measured by surface plasmon resonance (SPR) G-actin directly interacts with PMCA with an apparent 1:1 stoichiometry in the presence of Ca2+ with an apparent affinity in the micromolar range. As assessed by the photoactivatable probe [125I]TID-PC/16, the association of PMCA to actin produced a shift in the distribution of the conformers of the pump towards a calmodulin-activated conformation. G-actin stimulates Ca2+-ATPase activity of the enzyme when incubated under polymerizing conditions displaying a cooperative behavior. The increase in the Ca2+-ATPase activity was related to an increase in the apparent affinity for Ca2+ and an increase in the phosphoenzyme levels at steady-state. Although SPR experiments revealed only one binding site for G-actin, results clearly indicate that more than one molecule of G-actin was needed for a regulatory effect on the pump. Polymerization studies showed that the experimental conditions are compatible with the presence of actin in the first stages of assembly. Altogether, these observations suggest that the stimulatory effect is exerted by short oligomers of actin. The functional interaction between actin oligomers and PMCA represents a novel regulatory pathway by which the cortical actin cytoskeleton participates in the regulation of cytosolic Ca2+ homeostasis.