The cross-linking of tubulin with imidoesters

Tubulin was reacted with a monofunctional imidoester, ethyl acetimidate, and three bifunctional imidoesters ranging in extension from 5 to 10 A. Extensive cross-linking was found to occur with the three bifunctional reagents resulting in the formation of dimers, trimers, tetramers, pentamers, and hexamers. In addition, a similar cross-linking patterns was observed with the monofunctional reagent. This type of cross-linking is rarely seen when proteins are reacted with imidoesters. Given that the cross-linking span of ethyl acetimidate is only 3 A it is reasonable to infer that there are nucleophilic groups in close proximity within the tubulin dimer. Amidinated tubulin is still capable of assembling into microtubules.