Binding of a tau-like protein of Xenopus laevis to microtubules: a fluorescence correlation analysis

JUAN ANGIOLINI; DIANA WETZLER; CARLA PALLAVICINI; LUCIANA BRUNO; VALERIA LEVI

Congreso; XLI Reunión Anual de la Sociedad Argentina de Biofísica; 2012

Microtubules are decorated with a family of proteins called MAPs (microtubule associated proteins) that carry out a wide range of functions, from stabilizing and destabilizing microtubules to regulating spacing and mediating interaction of microtubules with other proteins. Tau protein is one of the most abundant MAPs in neurons and has a central role in neurodegenerative diseases, such as Alzheimer's. Previous works showed that molecular motors and tau proteins share the same binding site on microtubules suggesting that tau may affect transport mediated by molecular motors. In this direction, it has been shown in in vitro experiments that tau interferes with the binding of kinesin to the microtubule. However, these experiments were done in conditions far from those observed in cells In this work we explored the binding of XTP (a tau-like protein from Xenopus laevis melanophores) to microtubules and its relevance to transport mediated by molecular motors. We acquired confocal movies of regions of cells expressing XTP-GFP and tracked in these movies regions of microtubules to obtain their fluorescence as a function of time. We could determine the autocorrelation function in different regions of each microtubule and fitted the resulting data with a model that consider that fluctuations are due to the binding/unbinding of XTP to the microtubule. We could observe that microtubules do not bind XTP homogenously showing submicrometer-sized regions with high affinity for the MAP protein. To further explore the relevance of these regions to the transport, we generated red-fluorescent endosomes and tracked simultaneously the binding of XTP to microtubule and the motion of these organelles.