The cytoskeletal infrastructure underlies fundamental processes of cellular life such as: motility, division, morphology, and intracellular transport. The microtubule (MT) component of the cytoskeleton is an inherently dynamic structure and yet the MTs are stabilized for more than 100 years within the nervous system of some individuals. The stabilized MTs both maintain synaptic connections and serve as a highway for the intracellular transport required for synapsis function. These processes are sensitive to the effects of aging and correlated with the loss of functional synapsis over time. Additionally, alterations of the cytoskeleton are characteristic to neurodegenerative diseases such as Alzheimer's and Parkinson's disease, which typically manifest later in life. The research in this proposal is aimed at obtaining some of the first structural characterization of the proteins involved in stabilizing and trafficking upon the MT highway. The protein tau is used by neurons to stabilize its MTs and is also one of two major protein deposits associated with Alzheimer's disease. Historically, structural information on tau has be lacking due to its conformational flexibility. The approach here is to solve the structure of tau bound to mapmodulin, which will lock tau into a single conformation and circumvent the aggregation tendencies of tubulin. The structural information will complement other studies and provide a coherent structural framework for understanding the interactions between the different conformational states of tau and microtubules providing new venues for drug design and the prevention or correction of tau deposition. Currently there is an absence of structural information regarding interactions between MTs and intracellular transport. I propose to initiate studies on several additional MT binding domains in order to clarify at the molecular level the interactions involved in microtubule nucleation, growth, reduction, severing, stabilization, and regulation, that are required for intracellular transport.