DIRECT VISUALIZATION OF THE MICROTUBULE LATTICE SEAM BOTH IN-VITRO AND IN-VIVO

Citation
M. Kikkawa et al., DIRECT VISUALIZATION OF THE MICROTUBULE LATTICE SEAM BOTH IN-VITRO AND IN-VIVO, The Journal of cell biology, 127(6), 1994, pp. 1965-1971
Citations number
29
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Cell Biology
Journal title
ISSN journal
0021-9525
Volume
127
Issue
6
Year of publication
1994
Part
2
Pages
1965 - 1971
Database
ISI
SICI code
0021-9525(1994)127:6<1965:DVOTML>2.0.ZU;2-R
Abstract
Microtubules are constructed from alpha- and beta-tubulin heterodimers that are arranged into protofilaments. Most commonly there are 13 or 14 protofilaments. A series of structural investigations using both el ectron microscopy and x-ray diffraction have indicated that there are two potential lattices (A and B) in which the tubulin subunits can be arranged. Electron microscopy has shown that kinesin heads, which bind only to beta-tubulin, follow a helical path with a 12-nm pitch in whi ch subunits repeat every 8-nm axially, implying a primarily B-type lat tice. However, these helical symmetry parameters are not consistent wi th a closed lattice and imply that there must be a discontinuity or '' seam'' along the microtubule. We have used quick-freeze deep-etch elec tron microscopy to obtain the first direct evidence for the presence o f this seam in microtubules formed either in vivo or in vitro. In addi tion to a conventional single seam, we have also rarely found microtub ules in which there is more than one seam. Overall our data indicates that microtubules have a predominantly B lattice, but that A lattice b onds between tubulin subunits are found at the seam. The cytoplasmic m icrotubules in mouse nerve cells also have predominantly B lattice str ucture and A lattice bonds at the seam. These observations have import ant implications for the interaction of microtubules with MAPs and wit h motor proteins, and for example, suggest that kinesin motors may fol low a single protofilament track.