a,b-Tubulin

PDB file 1JFF

This file depicts the bovine tubulin heterodimer, determined by electron diffraction analysis of 2-D crystals (sheets) of tubulin induced by Zn⁺⁺.  a-Tubulin has bound GTP, while b-tubulin has bound GDP plus taxol. This data file, published by J. Lowe, H. Li, K. H. Downing, & E. Nogales in 2001, is a refinement of an earlier published structure.

Suggested display options:

Color chain and display as cartoon.
Select hetero-ligand, display as spacefill, and color CPK.
Identify the two nucleotides and taxol.
Note the position of GTP at the a-b interface.
Look for the loop on b-tubulin that blocks release or exchange of GTP on a-tubulin.

Examine the nucleotide binding pocket: Select protein-sheet and specify a different color, to visualize the b-sheet adjacent to the nucleotide binding site on each tubulin. 
How does this compare to structure of the myosin nucleotide-binding site?

Use the command line to select 142-148, the tubulin signature sequence GGGTGSG.
Visualize the position of these residues relative to the GDP or GTP.
Note the difference in structure of this "P loop" between a and b tubulin.
Why might Mg⁺⁺ be bound to a but not b tubulin?
What residue might H-bond with the terminal phosphate if the bound nucleotide on b-tubulin were changed to GTP?

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