Op18/stathmin caps a kinked protofilament-like tubulin tetramer.
Oncoprotein 18/stathmin (Op18), a regulator of microtubule dynamics, was recombinantly expressed and its structure and function analysed. We report that Op18 by itself can fold into a flexible and extended alpha-helix, which is in equilibrium with a less ordered structure. In complex with tubulin, however, all except the last seven C-terminal residues of Op18 are tightly bound to tubulin. Digital image analysis of Op18:tubulin electron micrographs revealed that the complex consists of two longitudinally aligned alpha/beta-tubulin heterodimers. The appearance of the complex was that of a kinked protofilament-like structure with a flat and a ribbed side. Deletion mapping of Op18 further demonstrated that (i) the function of the N-terminal part of the molecule is to 'cap' tubulin subunits to ensure the specificity of the complex and (ii) the complete C-terminal alpha-helical domain of Op18 is necessary and sufficient for stable Op18:tubulin complex formation. Together, our results suggest that besides sequestering tubulin, the structural features of Op18 enable the protein specifically to recognize microtubule ends to trigger catastrophes.
Steinmetz
M O
MO
M.E. Müller Institute for Microscopy, Biozentrum, University of Basel, CH-4056 Basel, Switzerland.
Kammerer
R A
RA
Jahnke
W
W
Goldie
K N
KN
Lustig
A
A
van Oostrum
J
J
D001483:Base Sequence; D002942:Circular Dichroism; D017931:DNA Primers / Q000235:genetics; D006801:Humans; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy; D008854:Microscopy, Electron; D017348:Microscopy, Electron, Scanning Transmission; D008868:Microtubule Proteins; D008870:Microtubules / Q000737:chemistry / Q000648:ultrastructure; D008954:Models, Biological; D010750:Phosphoproteins / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D050777:Stathmin; D014404:Tubulin / Q000737:chemistry* / Q000648:ultrastructure
D017931:DNA Primers; D046911:Macromolecular Substances; D008868:Microtubule Proteins; D010750:Phosphoproteins; D011994:Recombinant Proteins; C493995:STMN1 protein, human; D050777:Stathmin; D014404:Tubulin