Periodic crosslinking of microtubules by cytoplasmic microtubule-associated and microtubule-corset proteins from a trypanosomatid.

The dominant element in the cytoskeleton of Crithidia fasciculata is a peripheral corset of microtubules enclosing the cell body and closely underlying the plasma membrane. A lateral spacing of 50 nm is maintained by crosslinks, and microtubules may also be linked to the plasma membrane. We have characterized groups of polypeptides that associate with microtubules polymerized in vitro from the cytoplasm, or that are associated with the corset complex. They differ except for one of Mr 33,000 present in both groups. The corresponding native corset protein appears to be a dimer of Mr 66,000. These protein(s) copolymerize with brain tubulin, and the resultant polymer consists of pairs or small parallel bundles of microtubules, joined by periodic crosslinks spaced about 8.5 nm apart.