User Stories:ROP four-helix bundle

Crystallographic details

Parameter	Value	Comment
Space Group	C2
Unit Cell	92Å 24Å 64Å 90° 130° 90°	small
Resolution	2.9Å	average
Solvent Content	~50%	average
ASU Contents	4×26-residue helix	two helix-turn-helix motifs
Model Quality	1.0Å r.m.s.	Estimate - polyalanine helix
Anomalous atoms	N/A
Wavelength	N/A

Story

The A31P mutant of ROP forms a helix–turn–helix motif that homodimerizes to form a four-helix bundle. The asymmetric unit contains two copies of the helix–turn–helix motif. The structure was originally solved with a 26-residue polyalanine single helix as the model and an extremely computationally intensive 23- dimensional Monte-Carlo search implemented in the program Queen of Spades.

The r.m.s. deviation for ROP is given as 1.0 Å, since the sequence identity of the polyalanine helix is not a valid estimation of the r.m.s. deviation between the polyalanine helix and the backbone atoms of the ROP structure. The r.m.s. deviation value of 1.0 Å is a reasonable guess.

Phaser produces eight solutions after a tree search with hundreds of branches, especially in the search for the second of the four helices. The eight solutions are nearly identical, differing only in the registration of the model to the structure helices (i.e. the Cα residues slip up or down the helix). All eight solutions generate a complete structure after model building with ARP/wARP. Although many potential solutions are stored in the intermediate stages of the search, the search itself is not computationally intensive.

Keyword script(s)

MODE MR_AUTO
HKLIN beta_blip.mtz
LABIN F=Fobs SIGF=Sigma
ENSEMBLE BETA PDB beta.pdb ID 100
ENSEMBLE BLIP PDB blip.pdb ID 100
SEARCH ENSEMBLE BETA
SEARCH ENSEMBLE BLIP

Reference(s)

Solving structures of protein complexes by molecular replacement with Phaser

McCoy AJ

Acta Cryst. (2007). D63, 32-41