Interaction of brain mitochondria with microtubules reconstituted from brain tubulin and MAP2 or TAU

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Abstract
To explore the behaviour of microtubule‐associated proteins, MAP2 and TAU in the interactions of mitochondria with microtubules, an homologous acellular system has been reconstituted with organelles isolated from rat brain. We have established a quantitative in vitro binding assay based on the cosedimentation of 125I‐labeled microtubules with mitochondria. We found that binding of microtubules to mitochondria was concentration dependent and saturable. Binding was insensitive to ATP. A comparison of taxol‐stabilized microtubules prepared from MAP‐free tubulin or tubulin coated with TAU or MAP2 showed that the microtubule‐associated proteins diminished, or reduced to background levels, the formation of complexes with mitochondria. In contrast, the amount of MAP‐free taxol microtubules that cosedimented with mitochondria increased two‐ and six‐fold when mitochondria were coated with MAP2 or TAU. These studies suggest that the two major brain MAPs could have a crosslinking or a spacing role, depending on their organelle localization.