Synergistic effect of Pb(2+) and phosphatidylinositol 4,5-bisphosphate on C2 domain-membrane interactions.

ABSTRACT: Ca(2+)-responsive C2 domains are peripheral membrane modules that target their host proteins to anionic membranes upon binding Ca(2+) ions. Several C2 domain-containing proteins, such as protein kinase C isoenzymes (PKCs), have been identified as molecular targets of Pb(2+), a known environmental toxin. We demonstrated previously that the C2 domain from PKC? (C2?) binds Pb(2+) with high affinity and undergoes membrane insertion in the Pb(2+)-complexed form. The objective of this work was to determine the effect of phosphatidylinositol 4,5-bisphosphate (PIP(2)) on the C2?-Pb(2+) interactions. Using nuclear magnetic resonance (NMR) experiments, we show that Pb(2+) and PIP(2) synergistically enhance each other's affinity for C2?. Moreover, the affinity of C2? for PIP(2) increases upon progressive saturation of the metal-binding sites. Combining the NMR data with the results of protein-to-membrane Förster resonance energy transfer and vesicle sedimentation experiments, we demonstrate that PIP(2) can influence two aspects of C2?-Pb(2+)-membrane interactions: the affinity of C2? for Pb(2+) and the association of Pb(2+) with the anionic sites on the membrane. Both factors may contribute to the toxic effect of Pb(2+) resulting from the aberrant modulation of PKC? activity. Finally, we propose a mechanism for Pb(2+) outcompeting Ca(2+) from membrane-bound C2?.

SUBMITTER: Morales KA 

PROVIDER: S-EPMC3565054 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature