ausblenden:
Schlagwörter:
Actins/*metabolism; Animals; Binding Sites/physiology; Cells, Cultured; Centrifugation; DNA Primers; Electrophoresis, Polyacrylamide Gel; Immunohistochemistry; Microscopy, Electron; Microtubule-Associated Proteins/*metabolism; Microtubules/*metabolism/ultrastructure; Morphogenesis/physiology; Neurons/*metabolism/physiology; Recombinant Fusion Proteins/metabolism; tau Proteins/*metabolism
Zusammenfassung:
BACKGROUND: MAP2 and tau are abundant microtubule-associated proteins (MAPs) in neurons. The development of neuronal dendrites and axons requires a dynamic interaction between microtubules and actin filaments. MAPs represent good candidates to mediate such interactions. Although MAP2c and tau have similar, well-characterized microtubule binding activities, their actin interaction is poorly understood. RESULTS: Here, we show by using a cosedimentation assay that MAP2c binds F-actin. Upon actin binding, MAP2c organizes F-actin into closely packed actin bundles. Moreover, we show by using a deletion approach that MAP2c's microtubule binding domain (MTBD) is both necessary and sufficient for both F-actin binding and bundling activities. Surprisingly, even though the MAP2 and tau MTBDs share high sequence homology and possess similar microtubule binding activities, tau is unable to bind or bundle F-actin. Furthermore, experiments with chimeric proteins demonstrate that the actin binding activity fully correlates with the ability to promote neurite initiation in neuroblastoma cells. CONCLUSIONS: These results provide the first demonstration that the MAP2c and tau MTBD domains exhibit distinct properties, diverging in actin binding and neurite initiation activities. These results implicate a novel actin function for MAP2c in neuronal morphogenesis and furthermore suggest that actin interactions could contribute to functional differences between MAP2 and tau in neurons.
