ID #2291

What exactly is the purpose of alpha tubulin? If its GTP doesn't get hydrolyzed, what purpose does it have to the microtubule? Does it provide structural support, or is it just a place for the beta tubulin to dock?

Your question is a good one. Essentially, tubulin must be in a dimer in order to function. A single beta tubulin monomer will be unable to polymerize with other beta tubulin monomers to form a microtubule. Only tubulin heterodimers consisting of both alpha and beta subunits can be incorporated into microtubules. It is common for many proteins to be functional only when they are in a complex with other polypeptides. I found a scientific manuscript about protein dimerization that suggests that it is more economical for a cell to make dimeric proteins because the cell does not need to encode as many genes to make proteins, and a protein with multiple subunits will fold more easily and more readily than one large protein. 

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