0 8.0 × see more 10-4 GFxQG 11 2.32 4.0 × 10-3 GxxDGFxxG 4 3.73 4.7 × 10-3 GHxxGxxxGxAxG 4 3.66 5.5 × 10-3 GQxxGYxxG 4 3.41 9.1 × 10-3 GxQxGxxQG 5 2.92 1.2 × 10-2 GLxxGRxxG 5 2.78 1.7 × 10-2 GxxKGxxxGxxxGxxxGxExG 4 2.86 2.8 × 10-2 GYxxGFxxG 8 2.01 4.4 × 10-2 GYxxGLxxG 8 2.01 4.4 × 10-2 GLxQG 7 2.07 4.9 × 10-2 Pairs of amino acids that occur together at a significantly higher frequency than would be expected by chance (given their individual frequencies) are shown. 1The number of times that this particular pattern occurs. 2The number of times more often than would

be expected by chance that this pattern occurs. The P-value is the result of a χ2 test; see the experimental procedures section for full details. As expected, most of the significant patterns found in Table 1 involve residues that are nearby in the primary sequence, although there is an important exception. The most significant correlation is GxAxGxxxGxAxG, which is surprising given that it is a longer-range pattern. It is possible that the Ala residues in the x2 positions contribute to helical stability via hydrophobic interactions or by some other mechanism. Some correlations are readily explicable; for instance, the pattern GQxxGYxxG seems plausible, as the NE2 amide

hydrogen of the Gln residue at x1 should be able to either donate a hydrogen bond to the Tyr residue OH or provide its N-H group to make an amino-aromatic interaction. Furthermore, the NE2 amide hydrogen of a Gln residue in position x1 Evofosfamide can also donate a hydrogen bond to the backbone carbonyl oxygen of the first Gly residue in the neighbouring twofold related GxxxG helix segment presuming standard GxxxG helix dimerization [26]. However, other patterns are more difficult to Staurosporine molecular weight explain. For instance, the pattern GYxxGFxxG is found twice as often as would be expected by chance, but the Phe and Tyr side chains are unlikely to interact directly with each other, as both side chains would presumably

be in a χ1 = 180° conformation favoured by aromatic residues in helices, preventing van der Waals stacking of the aromatic rings. The strong positive correlation may indicate Metformin that the combination of these two residues in these positions is conducive to forming helix-helix interactions through close contacts of the aromatic side chain on one helix with the glycine backbone atoms on the adjacent helix, again assuming standard GxxxG helix dimerization. Identifying glycine repeats in the helices of other proteins A set of 7,963 proteins were downloaded from the PDB, and the helices from each protein were examined to determine the presence and length of any glycine repeats. Because GxxxG is the dominant motif in FliH proteins, these helices were examined only for GxxxGs; AxxxGs and GxxxAs were ignored. This analysis is similar to that performed by Kleiger et al. [26], who examined another non-redundant PDB set and found that 1.