engleski

Domain analysis of cortexillin I: actin bundling, PIP2-binding and the rescue of cytokinesis

Cortexillins are actin-bundling proteins that form a parallel two-stranded coiled-coil rod. Actin-binding domains of the alpha-actinin/spectrin type are located N-terminal to the rod and unique sequence elements are found in the C-terminal region. Domain analysis ill vitro revealed that the N-terminal domains are not responsible for the strong actin-filament bundling activity of cortexillin I. The strongest activity resides in the C-terminal region. Phosphatidylinositol 4, 5-bisphosphate (PIP2) suppresses this bundling activity by binding to a C-terminal nonapeptide sequence. These data define a new PIP2-regulated actin-bundling site. In vivo the PIP2-binding motif enhances localization of a C-terminal cortexillin I fragment to the cell cortex and improves the rescue of cytokinesis. This motif is not required, however, for translocation to the cleavage furrow. A model is presented proposing that cortexillin translocation is based on a mitotic cycle of polar actin polymerization and midzone depolymerization.

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