Microtubules are long protein filaments that form an important part of the cell cytoskeleton. They are formed from polymers of a protein called tubulin - first tubulin forms dimers, each consisting of one alpha and one beta subunit, and then these dimers polymerise head-to-tail to form structures called protofilaments. The microtubules are hollow tubes formed from assemblies of parallel protofilaments. Several proteins collectively known as microtubule associated proteins (MAPs) associate with these microtubules and stabilise - or occasionally destabilise - different forms.
Doublecortin is a MAP that stabilises the most commonly found type of microtubule, which is composed from thirteen protofilaments. Mutations in both proteins that destabilise the interaction between them can cause devastating neurological diseases. A recent paper by Carolyn Moores, an electron microscopist working at Birkbeck, has highlighted details of the interaction between these proteins.
You can read a summary of this paper here (PDF format). This is one of a series of summaries of high impact papers by Birkbeck scientists that I have written for the website of the Institute of Structural and Molecular Biology, which links researchers in these disciplines at Birkbeck with those at UCL.
If you have time once you have read the summary you may explore the structures of these proteins further by downloading the atomic coordinate files that were "docked" into the electron density in this paper from the PDB. The PDB entry used for the alpha-beta tubulin dimer structure is 1JFF and the one used for the doublecortin domain that is bound to tubulin is 1MJD.