The two parts of the Coronavirus beginner puzzle. The binder part can be freely designed and moved. The target is actually part of the coronavirus, and is mostly locked in place.
The new Beginner Puzzle (<150): Coronavirus presents an easier introduction working on coronavirus in Foldit.
Unlike the intermediate-level coronavirus puzzles, the beginner version starts the the binder part already designed. Players can move the binder around, and use Foldit tools like mutate, shake, wiggle and remix to improve it.
The starting design in the beginner coronavirus design puzzle is based on how coronavirus binds to human cells. It's part of the ACE2 enzyme (angiotensin-converting enzyme 2), found on the surface of many cells. ACE2 is the target of the coronavirus spike protein.
The beginner puzzle aims to turn the table, making the spike protein the target.
As in the other coronavirus puzzles, the gray part of the beginner puzzle is a portion of the coronavirus, a small section of the "spike" protein that allows the virus to bind to human cells. The backbone of the target is locked, meaning it can't move or change shape. Many of the sidechains of the target are unlocked. These sidechains are in the "binding site", where the coronavirus normally attaches to a human cell. These moveable sidechains are normally colorful, which the locked sidechains are gray.
The goal in all the coronavirus puzzles is to find a binder shape that's a good fit for the binding site on the target. The binder should form hydrogen bonds with the target, ideally with the moveable sidechains.
A good coronavirus binder should score well in Foldit, meaning it has a good core, where most of the hydrophobics are located, and few voids, empty areas inside the protein. (Clashes are also bad, but usually wiggle and shake take care of them.)
Like the intermediate-level (translation: very difficult level) coronavirus puzzles, players can add up to 10 segments in the beginner puzzle. Unlike the intermediate puzzles, there's no penalty for adding segments in the beginner puzzle.
In all the coronavirus puzzles, players can use all the Foldit tools, either manually or through recipes. One exception is the rebuild tool, which is disabled on most recent design puzzles, including the coronavirus puzzles. The remix tool is the alternative to rebuild. Remix has a user-friendly interface (very unlike rebuild), and it improves the chances that designs will fold up on their own.
One thing to note is that the binder and the target are two separate protein chains. Players can make hydrogen bonds between the two chains, but Foldit doesn't allow joining them with a peptide bond, which would make them into one chain.