Binding of alpha-fodrin to gamma-tubulin accounts for its role in the inhibition of microtubule nucleation

Non-erythroid spectrin or fodrin is present as part of the gamma-tubulin ring complex (gamma-TuRC) in brain tissue and brain derived cells. Here, we show that fodrin, which is otherwise known for providing structural support to the cell membrane, interacts directly with gamma-tubulin within the gamma-TuRC through a GRIP2-like motif. Turbidometric analysis of microtubule polymerization with nucleation-potent gamma-TuRC isolated from HEK-293 cells that lack fodrin and the gamma-TuRC from goat brain that contains fodrin shows inefficiency of the latter to promote nucleation. The involvement of fodrin was confirmed by the reduction in the microtubule polymerization efficiency of HEK-293 derived gamma-TuRCs upon addition of purified brain fodrin. Thus, the interaction of fodrin with gamma-tubulin is responsible for its inhibitory effect on gamma-tubulin mediated microtubule nucleation.