Hoenger Lab
University of Colorado at Boulder
Department of Molecular, Cellular and Developmental Biology

Structural and Functional Investigations
into Cytoskeletal Assemblies by
Cryo Electron Microscopy
and 3D Image Analysis

Research:: Microtubule Associated Proteins

Microtubules associated proteins, MAPs, mediate the dynamic processes of microtubules. MAPs stabilize and destabilize tubules, are associated with the coupling of molecular motors and microtubules, and play critical roles in nuclear spindle formation.

End Binding 1 proteins such as Malp3 binds at microtubule seams, TAU fortifies microtubules in nerve axons. HURP, NuSAP, and TPX2 are other MAPs that mediate spindle formation.

The examples above are of end binding proteins EB1, this particular example is Mal3p from yeast cells. This protein stabilizes microtubules along the microtubule lattice seam. Occasionally microtubules can be found where Malp3 aligns in two adjacent rows indicating that there are two seams side by side. Most likely there are adjacent to one another as modeled in H. A 13 protofilament microtubule would need to compensate this double seam with a third seam as shown above.
High-resolution model of the kinesin–tubu­lin complex in ribbon representation and the proposed major interaction site of htau40 (red wire frame). A, View from outside the MT cylinder. B, Tangential view from a point between two protofilaments. According to cross-correlation studies with reconstructions obtained from MTs decorated with kinesin, the major tau-binding site locates to tubulin, in close proximity to helices 11 and 12. However, the volume indicated in red accounts for less than 5% of the mass of htau40, the remainder is distributed non-periodically. The exposed position of this site, near the outer protofilament ridge and almost between two protofilaments, suggests that tau may also bind across protofilaments (see also Figures 5 and 6B).

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