Interaction partners of parkin: Tubulin/microtubules and beta-subunit of sodium(+), potassium(+)-ATPase
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Parkin plays an important role in the degradation of misfolded or damaged proteins. The mutation of parkin is the most prevalent genetic factor causing familial PD. We studied the interaction of parkin with the β1 and β2 subunit of Na + , K + -ATPase, which appeared as binding partners of parkin in the yeast two-hybrid system. However, the co-immunoprecipitation assay was not supportive for the interaction. In the ubiquitination assay, parkin co-transfection resulted in a subtle increase in the amount of proteins that might represent the ubiquitinated β1 and β2 subunits. The tight binding of parkin with in vitro assembled microtubules was shown in various protein manipulation methods. Furthermore, in vitro protein crosslinking studies suggested a close interaction of parkin with β-tubulin. Three separate domains can be co-immunoprecipitated with tubulin heterodimers, be co-assembled into microtubules in vitro and protect against colchicine-induced microtubule depolymerization in COS-7 cells. So the tight binding of parkin with tubulin heterodimers and microtubules could be accounted for by the multiple interaction sites of parkin with both tubulin heterodimers and microtubules. The binding of parkin or parkin domains with tubulin heterodimers/microtubules and stabilization of microtubules by parkin do not depend on the E3 ligase activity of parkin. The stabilization of microtubules by parkin may contribute to the integrity of microtubule network. In addition to facilitating the turn-over of tubulins, parkin may also be involved in connecting the ubquitin-proteasome pathway with microtubules.