the problem with tubulin is its hetero polymer and the alpha and beta subunits, in higher mammalians even more subunits and more complex. the commercially available proteins are not purified to that extent that you can use it for crystallization. moreover the complex is too flexible to crystallize. a best way of doing it trying tubulin made from one subunit only. if thats not possible, try doing limited proteolysis on complex and reduce the complex to minimal domains which is stable enough to crystallize. there are plenty of publications available on protein protein complex crystals. good Luck. 

I agree with the previous poster. Tubulin has the propensity to self assemble into microtubules and therefore without disrupting its physiological interfaces, it is therefore unlikely to crystallise. Most structural analyses of tubulin have therefore centered on cryoEM tomography analysis of MTs. Alternatively, it is possible to exploit tubulin's natural interfaces to make 2-d sheets under certain conditions, on which electron diffraction can be carried out. To crystallise tubulin you would need to first find a way to stabilise a smaller homogenous "building block". There is an interesting example of such an approach here:

http://www.sciencemag.org/content/339/6119/587.long