Foldit bands can also be used to push things apart, which is difficult with real rubber bands.
There are two types of bands. One type of band is drawn from segment to segment in the protein. The other type of band starts on a segment, but ends at a point in space. This type of band is called a "band in space" or BiS. The name spaceband is also used, and will be used in this article.
Banding rules Edit
All bands must start on a segment. The band may start on the segment's backbone, or on one of the atoms in the segment's sidechain. A segment-to-segment band must end on the backbone or sidechain of a different segment.
A spaceband must also start on the backbone or sidechain of a segment. A spaceband ends at an arbitrary point in space. While Foldit doesn't show any spatial coordinates, the "space" end of a spaceband seems to be anchored to a specific point in space. The ends of a segment-to-segment band, in contrast, tend to move around in space as the protein changes shape.
One other restriction applies to symmetry puzzles. These puzzles have a main protein, and one or more symmetric copies of the main protein. All bands must begin on a segment of the main protein. A segment-to-segment band can be drawn from the main protein to a segment on one of the symmetric copies.
Drawing bands Edit
As noted above, bands must start on the backbone or sidechain of a segment.
In the original Foldit interface, band are drawn with shift left-click and drag. Or, with a three-button mouse, middle-click and drag. The original interface must be in pull mode to draw a band.
In the selection interface, bands are drawn with a right-click and drag. Control or command left-click and drag are also available.
If sidechains are hidden, new bands can only be started on the protein's backbone. Use the sidechain view options "Show Stubs" or "Show All" for banding sidechains.
The default "Cartoon" (and its slimmer sibling "Cartoon Thin") protein views limit which atoms can be banded. No backbone atoms are shown. Only the non-hydrogen atoms of the sidechain are shown, so only these can be banded.
Other protein view options such as "Stick+H" show additional backbone atoms, and make hydrogens visible for banding. Recipes can also band to any atom.
Attributes of bands Edit
Both segment-to-segment bands and spacebands have a strength attribute, which defaults to 1.0. Band strength can be adjusted from 0.5 to 1.5 in the Foldit client. Recipes can change band strength from 0.0 to 10.0.
Segment-to-segment bands have two different length properties. The first is simply the current length of the band. The second is called the "goal length", which is how long the band wants to be. The current length can't be changed directly, but it may change if the banded segments move relative to each other. The default goal length is 3.5, and goal length can be changed from 0.0 to 20.0 in the client. Recipes can set a goal length up to 10,000.
Band length is measured in angstroms, a unit of length used in protein analysis.
When a segment-to-segment band's goal length is shorter than its current length, the band tends to pull the two segments together.
When the band's goal length is longer than its current length, it tends to push the segments apart.
A segment-to-segment band has two conical goal length indicators. They're positioned between the segments when the goal length is less than or equal to the band's current length. The length cones appear on thin projections beyond the segments when the goal length is greater than the current length.
Spacebands are slightly different. Spacebands have length and goals length attributes just like segment-to-segment bands. The default goal length of a spaceband is 0.0. This means that, by default, a spaceband tends to pull the segment towards a point in space. Any goal shorter than the current length also pulls toward the point in space. A goal length longer than the current length tends to push segment away from the point in space.