1 research outputs found
Membrane Order Is a Key Regulator of Divalent Cation-Induced Clustering of PI(3,5)P<sub>2</sub> and PI(4,5)P<sub>2</sub>
Although the evidence for the presence
of functionally important
nanosized phosphorylated phosphoinositide (PIP)-rich domains within
cellular membranes has accumulated, very limited information is available
regarding the structural determinants for compartmentalization of
these phospholipids. Here, we used a combination of fluorescence spectroscopy
and microscopy techniques to characterize differences in divalent
cation-induced clustering of PIĀ(4,5)ĀP<sub>2</sub> and PIĀ(3,5)ĀP<sub>2</sub>. Through these methodologies we were able to detect differences
in divalent cation-induced clustering efficiency and cluster size.
Ca<sup>2+</sup>-induced PIĀ(4,5)ĀP<sub>2</sub> clusters are shown to
be significantly larger than the ones observed for PIĀ(3,5)ĀP<sub>2</sub>. Clustering of PIĀ(4,5)ĀP<sub>2</sub> is also detected at physiological
concentrations of Mg<sup>2+</sup>, suggesting that in cellular membranes,
these molecules are constitutively driven to clustering by the high
intracellular concentration of divalent cations. Importantly, it is
shown that lipid membrane order is a key factor in the regulation
of clustering for both PIP isoforms, with a major impact on cluster
sizes. Clustered PIĀ(4,5)ĀP<sub>2</sub> and PIĀ(3,5)ĀP<sub>2</sub> are
observed to present considerably higher affinity for more ordered
lipid phases than the monomeric species or than PI(4)ĀP, possibly reflecting
a more general tendency of clustered lipids for insertion into ordered
domains. These results support a model for the description of the
lateral organization of PIPs in cellular membranes, where both divalent
cation interaction and membrane order are key modulators defining
the lateral organization of these lipids