Sequence analysis reveals a conserved extension in the capping enzyme of the alphavirus supergroup, and a homologous domain in nodaviruses

Table 2 Properties of known or selected, predicted membrane-binding, amphipathic α-helices in the MTase-GTase of the alto group

Genus	Species	Boundaries ¹ (aa)	Predicted secondary element(s)	Mean Hydrophobicity (<H>)	Hydrophobic moment (<μH>)	Charge (z)	Heliquest Discriminating factor (D) ²	Status
Alphavirus	Semliki Forest	245-264	αE’ and βH	0.44	0.28	+2	0.93	Experimentally proven, detected by Heliquest
Bromovirus	Brome mosaic	392-409	αH	0.54	0.27	+1	0.58	Experimentally proven, but not detected by Heliquest
Bromovirus	Brome mosaic	416-433	αI	0.60	0.30	+2	0.94	Predicted by Heliquest
Cucumovirus	Cucumber mosaic	446-468	αI	0.66	0.54	+3	1.50	Strongly predicted by Heliquest
Furovirus	Soil-borne wheat mosaic	291-312	βG, αE’ and βH	0.37	0.37	+4	1.67	Strongly predicted by Heliquest
Idaeovirus	Raspberry bushy dwarf	627-646	αI	0.7	0.57	+3	1.52	Strongly predicted by Heliquest

¹Helical wheel representations for these helices are in Additional file 1: Figure S9.
²The Heliquest Discriminating factor D is equal to 0.944 < μH > +0.33z. The helix is predicted as “potential” lipid-binding amphipathic α-helix if 0.68 < D < 1.34, and as a reliable one if D ≥ 1.34 (see Methods for details).