Molecular Dynamics of the Recruitment of Immunoreceptor Signaling Module DAP12 Homodimer to Lipid Raft Boundary Regulated by PIP2.

Abstract

Lipid raft microdomain of the plasma membrane is implicated in various biological and pathological processes. The involvement of lipid raft in T cell receptor (TCR) signal transduction has been widely studied, whereas the role of these structures in immunoreceptor signaling by DAP12 in natural killing (NK) cells remains largely unknown. Here, we demonstrate that phosphatidylinositol 4,5-bisphosphate (PIP2) lipid localized to lipid raft boundary in our coarse-grained (CG) model raft-forming membrane, and this negatively charged lipid recruits DAP12 homodimer into lipid raft boundary through protein-lipid interaction between the basic-rich regions and signaling immunoreceptor tyrosine-based activation motifs (ITAMs) of DAP12 and PIP2. Furthermore, our results reveal that the protein-lipid interaction can be disrupted by Ca2+, which competitively binds to PIP2 instead of DAP12. As a result, the cytoplasmic region of DAP12 homodimer is dissociated from the membrane back to the nonraft domain, and the ITAMs are exposed to allow further downstream signaling. These findings provide fundamental insights to understand the mechanism of signal transduction in NK cells regulated by membrane microenvironment.