3OKQ: Crystal Structure Of A Core Domain Of Yeast Actin Nucleation Cofactor Bud6

Formin proteins and their associated factors cooperate to assemble unbranched actin filaments in diverse cellular structures. The Saccharomyces cerevisiae formin Bni1 and its associated nucleation-promoting factor (NPF) Bud6 generate actin cables and mediate polarized cell growth. Bud6 binds to both the tail of the formin and G-actin, thereby recruiting monomeric actin to the formin to create a nucleation seed. Here, we structurally and functionally dissect the nucleation-promoting C-terminal region of Bud6 into a Bni1-binding "core" domain and a G-actin binding "flank" domain. The approximately 2-A resolution crystal structure of the Bud6 core domain reveals an elongated dimeric rod with a unique fold resembling a triple-helical coiled-coil. Binding and actin-assembly assays show that conserved residues on the surface of this domain mediate binding to Bni1 and are required for NPF activity. We find that the Bni1 dimer binds two Bud6 dimers and that the Bud6 flank binds a single G-actin molecule. These findings suggest a model in which a Bni1/Bud6 complex with a 2:4 subunit stoichiometry assembles a nucleation seed with Bud6 coordinating up to four actin subunits.
PDB ID: 3OKQDownload
MMDB ID: 93549
PDB Deposition Date: 2010/8/25
Updated in MMDB: 2012/12
Experimental Method:
x-ray diffraction
Resolution: 2.04  Å
Source Organism:
Similar Structures:
Biological Unit for 3OKQ: dimeric; determined by author and by software (PISA)
Molecular Components in 3OKQ
Label Count Molecule
Proteins (2 molecules)
BUD Site Selection Protein 6(Gene symbol: BUD6)
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB